diff --git a/pkg/execution/curve_encoder_test.go b/pkg/execution/curve_encoder_test.go
new file mode 100644
index 0000000..045d6a0
--- /dev/null
+++ b/pkg/execution/curve_encoder_test.go
@@ -0,0 +1,421 @@
+package execution
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewCurveEncoder(t *testing.T) {
+	encoder := NewCurveEncoder()
+	assert.NotNil(t, encoder)
+}
+
+func TestCurveEncoder_EncodeSwap(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID (first 4 bytes)
+	// exchange(int128,int128,uint256,uint256)
+	assert.Len(t, data, 4+4*32) // methodID + 4 parameters
+}
+
+func TestCurveEncoder_EncodeExchangeUnderlying(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	to, data, err := encoder.EncodeExchangeUnderlying(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID
+	// exchange_underlying(int128,int128,uint256,uint256)
+	assert.Len(t, data, 4+4*32)
+}
+
+func TestCurveEncoder_EncodeDynamicExchange(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	i := big.NewInt(0)
+	j := big.NewInt(1)
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	to, data, err := encoder.EncodeDynamicExchange(
+		i,
+		j,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID
+	// exchange(uint256,uint256,uint256,uint256)
+	assert.Len(t, data, 4+4*32)
+}
+
+func TestCurveEncoder_EncodeDynamicExchange_HighIndices(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	i := big.NewInt(2)
+	j := big.NewInt(3)
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	to, data, err := encoder.EncodeDynamicExchange(
+		i,
+		j,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestCurveEncoder_EncodeGetDy(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	i := big.NewInt(0)
+	j := big.NewInt(1)
+	amountIn := big.NewInt(1e18)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	to, data, err := encoder.EncodeGetDy(
+		i,
+		j,
+		amountIn,
+		poolAddress,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID
+	// get_dy(int128,int128,uint256)
+	assert.Len(t, data, 4+3*32)
+}
+
+func TestCurveEncoder_EncodeCoinIndices(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	tokenAddress := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	to, data, err := encoder.EncodeCoinIndices(
+		tokenAddress,
+		poolAddress,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID
+	// coins(uint256)
+	assert.Len(t, data, 4+32)
+}
+
+func TestCurveEncoder_GetCoinIndex(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	tests := []struct {
+		name          string
+		tokenAddress  common.Address
+		poolCoins     []common.Address
+		expectedIndex int
+		expectError   bool
+	}{
+		{
+			name:         "First coin",
+			tokenAddress: common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+			poolCoins: []common.Address{
+				common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+			},
+			expectedIndex: 0,
+			expectError:   false,
+		},
+		{
+			name:         "Second coin",
+			tokenAddress: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+			poolCoins: []common.Address{
+				common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+			},
+			expectedIndex: 1,
+			expectError:   false,
+		},
+		{
+			name:         "Third coin",
+			tokenAddress: common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+			poolCoins: []common.Address{
+				common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+			},
+			expectedIndex: 2,
+			expectError:   false,
+		},
+		{
+			name:         "Token not in pool",
+			tokenAddress: common.HexToAddress("0x0000000000000000000000000000000000000099"),
+			poolCoins: []common.Address{
+				common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+			},
+			expectedIndex: -1,
+			expectError:   true,
+		},
+		{
+			name:          "Empty pool",
+			tokenAddress:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+			poolCoins:     []common.Address{},
+			expectedIndex: -1,
+			expectError:   true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			index, err := encoder.GetCoinIndex(tt.tokenAddress, tt.poolCoins)
+
+			if tt.expectError {
+				assert.Error(t, err)
+				assert.Equal(t, tt.expectedIndex, index)
+			} else {
+				require.NoError(t, err)
+				assert.Equal(t, tt.expectedIndex, index)
+			}
+		})
+	}
+}
+
+func TestCurveEncoder_ZeroAddresses(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	tokenIn := common.Address{}
+	tokenOut := common.Address{}
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.Address{}
+	recipient := common.Address{}
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestCurveEncoder_ZeroAmounts(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(0)
+	minAmountOut := big.NewInt(0)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestCurveEncoder_LargeAmounts(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+
+	// Max uint256
+	amountIn := new(big.Int)
+	amountIn.SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
+	minAmountOut := new(big.Int)
+	minAmountOut.SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
+
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestCurveEncoder_LargeIndices(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	// Test with large indices (for pools with many coins)
+	i := big.NewInt(7)
+	j := big.NewInt(15)
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	to, data, err := encoder.EncodeDynamicExchange(
+		i,
+		j,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestCurveEncoder_NegativeIndices(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	// Negative indices (should be encoded as int128)
+	i := big.NewInt(-1)
+	j := big.NewInt(-2)
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	to, data, err := encoder.EncodeDynamicExchange(
+		i,
+		j,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestCurveEncoder_GetCoinIndex_MultipleTokens(t *testing.T) {
+	encoder := NewCurveEncoder()
+
+	// Test with a 4-coin pool (common for Curve)
+	poolCoins := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"), // WETH
+		common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"), // USDC
+		common.HexToAddress("0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9"), // USDT
+		common.HexToAddress("0xDA10009cBd5D07dd0CeCc66161FC93D7c9000da1"), // DAI
+	}
+
+	// Test each token
+	for i, token := range poolCoins {
+		index, err := encoder.GetCoinIndex(token, poolCoins)
+		require.NoError(t, err)
+		assert.Equal(t, i, index)
+	}
+}
+
+// Benchmark tests
+func BenchmarkCurveEncoder_EncodeSwap(b *testing.B) {
+	encoder := NewCurveEncoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _, _ = encoder.EncodeSwap(
+			tokenIn,
+			tokenOut,
+			amountIn,
+			minAmountOut,
+			poolAddress,
+			recipient,
+		)
+	}
+}
+
+func BenchmarkCurveEncoder_GetCoinIndex(b *testing.B) {
+	encoder := NewCurveEncoder()
+
+	tokenAddress := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	poolCoins := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+		common.HexToAddress("0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9"),
+		common.HexToAddress("0xDA10009cBd5D07dd0CeCc66161FC93D7c9000da1"),
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = encoder.GetCoinIndex(tokenAddress, poolCoins)
+	}
+}
diff --git a/pkg/execution/executor_test.go b/pkg/execution/executor_test.go
new file mode 100644
index 0000000..e1d399a
--- /dev/null
+++ b/pkg/execution/executor_test.go
@@ -0,0 +1,567 @@
+package execution
+
+import (
+	"context"
+	"log/slog"
+	"math/big"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/your-org/mev-bot/pkg/arbitrage"
+	mevtypes "github.com/your-org/mev-bot/pkg/types"
+)
+
+func TestDefaultExecutorConfig(t *testing.T) {
+	config := DefaultExecutorConfig()
+
+	assert.NotNil(t, config)
+	assert.Equal(t, uint64(1), config.ConfirmationBlocks)
+	assert.Equal(t, 5*time.Minute, config.TimeoutPerTx)
+	assert.Equal(t, 3, config.MaxRetries)
+	assert.Equal(t, uint64(2), config.NonceMargin)
+	assert.Equal(t, "fast", config.GasPriceStrategy)
+}
+
+func TestExecutor_getNextNonce(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:       logger,
+		currentNonce: 10,
+		nonceCache:   make(map[uint64]*PendingTransaction),
+	}
+
+	// Get first nonce
+	nonce1 := executor.getNextNonce()
+	assert.Equal(t, uint64(10), nonce1)
+	assert.Equal(t, uint64(11), executor.currentNonce)
+
+	// Get second nonce
+	nonce2 := executor.getNextNonce()
+	assert.Equal(t, uint64(11), nonce2)
+	assert.Equal(t, uint64(12), executor.currentNonce)
+}
+
+func TestExecutor_releaseNonce(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:       logger,
+		currentNonce: 10,
+		nonceCache:   make(map[uint64]*PendingTransaction),
+	}
+
+	// Release current nonce - 1 (should work)
+	executor.releaseNonce(9)
+	assert.Equal(t, uint64(9), executor.currentNonce)
+
+	// Release older nonce (should not work)
+	executor.currentNonce = 10
+	executor.releaseNonce(5)
+	assert.Equal(t, uint64(10), executor.currentNonce) // Should not change
+}
+
+func TestExecutor_trackPendingTransaction(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:     logger,
+		nonceCache: make(map[uint64]*PendingTransaction),
+	}
+
+	hash := common.HexToHash("0x123")
+	nonce := uint64(5)
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp",
+		InputAmount: big.NewInt(1e18),
+	}
+
+	executor.trackPendingTransaction(nonce, hash, opp)
+
+	// Check transaction is tracked
+	pending, exists := executor.nonceCache[nonce]
+	assert.True(t, exists)
+	assert.NotNil(t, pending)
+	assert.Equal(t, hash, pending.Hash)
+	assert.Equal(t, nonce, pending.Nonce)
+	assert.Equal(t, opp, pending.Opportunity)
+	assert.False(t, pending.Confirmed)
+	assert.False(t, pending.Failed)
+}
+
+func TestExecutor_GetPendingTransactions(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:     logger,
+		nonceCache: make(map[uint64]*PendingTransaction),
+	}
+
+	// Add pending transactions
+	executor.nonceCache[1] = &PendingTransaction{
+		Hash:      common.HexToHash("0x01"),
+		Confirmed: false,
+		Failed:    false,
+	}
+	executor.nonceCache[2] = &PendingTransaction{
+		Hash:      common.HexToHash("0x02"),
+		Confirmed: true, // Already confirmed
+		Failed:    false,
+	}
+	executor.nonceCache[3] = &PendingTransaction{
+		Hash:      common.HexToHash("0x03"),
+		Confirmed: false,
+		Failed:    false,
+	}
+
+	pending := executor.GetPendingTransactions()
+
+	// Should only return unconfirmed, non-failed transactions
+	assert.Len(t, pending, 2)
+}
+
+func TestExecutor_Stop(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:  logger,
+		stopCh:  make(chan struct{}),
+		stopped: false,
+	}
+
+	executor.Stop()
+
+	assert.True(t, executor.stopped)
+
+	// Calling Stop again should not panic
+	executor.Stop()
+	assert.True(t, executor.stopped)
+}
+
+func TestPendingTransaction_Fields(t *testing.T) {
+	hash := common.HexToHash("0x123")
+	nonce := uint64(5)
+	opp := &arbitrage.Opportunity{
+		ID: "test-opp",
+	}
+	submittedAt := time.Now()
+
+	pending := &PendingTransaction{
+		Hash:        hash,
+		Nonce:       nonce,
+		Opportunity: opp,
+		SubmittedAt: submittedAt,
+		LastChecked: submittedAt,
+		Confirmed:   false,
+		Failed:      false,
+		FailReason:  "",
+		Receipt:     nil,
+		Retries:     0,
+	}
+
+	assert.Equal(t, hash, pending.Hash)
+	assert.Equal(t, nonce, pending.Nonce)
+	assert.Equal(t, opp, pending.Opportunity)
+	assert.Equal(t, submittedAt, pending.SubmittedAt)
+	assert.False(t, pending.Confirmed)
+	assert.False(t, pending.Failed)
+	assert.Equal(t, 0, pending.Retries)
+}
+
+func TestExecutionResult_Success(t *testing.T) {
+	hash := common.HexToHash("0x123")
+	actualProfit := big.NewInt(0.1e18)
+	gasCost := big.NewInt(0.01e18)
+	duration := 5 * time.Second
+
+	result := &ExecutionResult{
+		Success:      true,
+		TxHash:       hash,
+		Receipt:      nil,
+		ActualProfit: actualProfit,
+		GasCost:      gasCost,
+		Error:        nil,
+		Duration:     duration,
+	}
+
+	assert.True(t, result.Success)
+	assert.Equal(t, hash, result.TxHash)
+	assert.Equal(t, actualProfit, result.ActualProfit)
+	assert.Equal(t, gasCost, result.GasCost)
+	assert.Nil(t, result.Error)
+	assert.Equal(t, duration, result.Duration)
+}
+
+func TestExecutionResult_Failure(t *testing.T) {
+	hash := common.HexToHash("0x123")
+	err := assert.AnError
+	duration := 2 * time.Second
+
+	result := &ExecutionResult{
+		Success:      false,
+		TxHash:       hash,
+		Receipt:      nil,
+		ActualProfit: nil,
+		GasCost:      nil,
+		Error:        err,
+		Duration:     duration,
+	}
+
+	assert.False(t, result.Success)
+	assert.Equal(t, hash, result.TxHash)
+	assert.NotNil(t, result.Error)
+	assert.Equal(t, duration, result.Duration)
+}
+
+func TestExecutorConfig_RPC(t *testing.T) {
+	config := &ExecutorConfig{
+		PrivateKey:         []byte{0x01, 0x02, 0x03},
+		WalletAddress:      common.HexToAddress("0x123"),
+		RPCEndpoint:        "http://localhost:8545",
+		PrivateRPCEndpoint: "http://flashbots:8545",
+		UsePrivateRPC:      true,
+	}
+
+	assert.NotEmpty(t, config.PrivateKey)
+	assert.NotEmpty(t, config.WalletAddress)
+	assert.Equal(t, "http://localhost:8545", config.RPCEndpoint)
+	assert.Equal(t, "http://flashbots:8545", config.PrivateRPCEndpoint)
+	assert.True(t, config.UsePrivateRPC)
+}
+
+func TestExecutorConfig_GasStrategy(t *testing.T) {
+	tests := []struct {
+		name       string
+		strategy   string
+		multiplier float64
+		maxIncrease float64
+	}{
+		{
+			name:       "Fast strategy",
+			strategy:   "fast",
+			multiplier: 1.2,
+			maxIncrease: 1.5,
+		},
+		{
+			name:       "Market strategy",
+			strategy:   "market",
+			multiplier: 1.0,
+			maxIncrease: 1.3,
+		},
+		{
+			name:       "Aggressive strategy",
+			strategy:   "aggressive",
+			multiplier: 1.5,
+			maxIncrease: 2.0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			config := &ExecutorConfig{
+				GasPriceStrategy:     tt.strategy,
+				GasPriceMultiplier:   tt.multiplier,
+				MaxGasPriceIncrement: tt.maxIncrease,
+			}
+
+			assert.Equal(t, tt.strategy, config.GasPriceStrategy)
+			assert.Equal(t, tt.multiplier, config.GasPriceMultiplier)
+			assert.Equal(t, tt.maxIncrease, config.MaxGasPriceIncrement)
+		})
+	}
+}
+
+func TestExecutor_calculateActualProfit(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger: logger,
+	}
+
+	// Create mock receipt
+	receipt := &types.Receipt{
+		GasUsed:           150000,
+		EffectiveGasPrice: big.NewInt(50e9), // 50 gwei
+	}
+
+	opp := &arbitrage.Opportunity{
+		GrossProfit: big.NewInt(0.2e18), // 0.2 ETH
+	}
+
+	actualProfit := executor.calculateActualProfit(receipt, opp)
+
+	// Gas cost = 150000 * 50e9 = 0.0075 ETH
+	// Actual profit = 0.2 - 0.0075 = 0.1925 ETH
+	expectedProfit := big.NewInt(192500000000000000) // 0.1925 ETH
+	assert.Equal(t, expectedProfit, actualProfit)
+}
+
+func TestExecutor_NonceManagement_Concurrent(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:       logger,
+		currentNonce: 10,
+		nonceCache:   make(map[uint64]*PendingTransaction),
+	}
+
+	// Simulate concurrent nonce requests
+	nonces := make(chan uint64, 10)
+
+	for i := 0; i < 10; i++ {
+		go func() {
+			nonce := executor.getNextNonce()
+			nonces <- nonce
+		}()
+	}
+
+	// Collect all nonces
+	receivedNonces := make(map[uint64]bool)
+	for i := 0; i < 10; i++ {
+		nonce := <-nonces
+		// Check for duplicates
+		assert.False(t, receivedNonces[nonce], "Duplicate nonce detected")
+		receivedNonces[nonce] = true
+	}
+
+	// All nonces should be unique and sequential
+	assert.Len(t, receivedNonces, 10)
+	assert.Equal(t, uint64(20), executor.currentNonce)
+}
+
+func TestExecutor_PendingTransaction_Timeout(t *testing.T) {
+	submittedAt := time.Now().Add(-10 * time.Minute)
+
+	pending := &PendingTransaction{
+		Hash:        common.HexToHash("0x123"),
+		SubmittedAt: submittedAt,
+		LastChecked: time.Now(),
+		Confirmed:   false,
+		Failed:      false,
+		Retries:     0,
+	}
+
+	timeout := 5 * time.Minute
+	isTimedOut := time.Since(pending.SubmittedAt) > timeout
+
+	assert.True(t, isTimedOut)
+}
+
+func TestExecutor_PendingTransaction_NotTimedOut(t *testing.T) {
+	submittedAt := time.Now().Add(-2 * time.Minute)
+
+	pending := &PendingTransaction{
+		Hash:        common.HexToHash("0x123"),
+		SubmittedAt: submittedAt,
+		LastChecked: time.Now(),
+		Confirmed:   false,
+		Failed:      false,
+		Retries:     0,
+	}
+
+	timeout := 5 * time.Minute
+	isTimedOut := time.Since(pending.SubmittedAt) > timeout
+
+	assert.False(t, isTimedOut)
+}
+
+func TestExecutor_PendingTransaction_MaxRetries(t *testing.T) {
+	pending := &PendingTransaction{
+		Hash:    common.HexToHash("0x123"),
+		Retries: 3,
+	}
+
+	maxRetries := 3
+	canRetry := pending.Retries < maxRetries
+
+	assert.False(t, canRetry)
+}
+
+func TestExecutor_PendingTransaction_CanRetry(t *testing.T) {
+	pending := &PendingTransaction{
+		Hash:    common.HexToHash("0x123"),
+		Retries: 1,
+	}
+
+	maxRetries := 3
+	canRetry := pending.Retries < maxRetries
+
+	assert.True(t, canRetry)
+}
+
+func TestExecutor_TransactionConfirmed(t *testing.T) {
+	pending := &PendingTransaction{
+		Hash:      common.HexToHash("0x123"),
+		Confirmed: true,
+		Failed:    false,
+		Receipt:   &types.Receipt{Status: types.ReceiptStatusSuccessful},
+	}
+
+	assert.True(t, pending.Confirmed)
+	assert.False(t, pending.Failed)
+	assert.NotNil(t, pending.Receipt)
+	assert.Equal(t, types.ReceiptStatusSuccessful, pending.Receipt.Status)
+}
+
+func TestExecutor_TransactionFailed(t *testing.T) {
+	pending := &PendingTransaction{
+		Hash:       common.HexToHash("0x123"),
+		Confirmed:  true,
+		Failed:     true,
+		FailReason: "transaction reverted",
+		Receipt:    &types.Receipt{Status: types.ReceiptStatusFailed},
+	}
+
+	assert.True(t, pending.Confirmed)
+	assert.True(t, pending.Failed)
+	assert.Equal(t, "transaction reverted", pending.FailReason)
+	assert.NotNil(t, pending.Receipt)
+	assert.Equal(t, types.ReceiptStatusFailed, pending.Receipt.Status)
+}
+
+func TestExecutorConfig_Defaults(t *testing.T) {
+	config := DefaultExecutorConfig()
+
+	// Test all default values
+	assert.Equal(t, uint64(1), config.ConfirmationBlocks)
+	assert.Equal(t, 5*time.Minute, config.TimeoutPerTx)
+	assert.Equal(t, 3, config.MaxRetries)
+	assert.Equal(t, 5*time.Second, config.RetryDelay)
+	assert.Equal(t, uint64(2), config.NonceMargin)
+	assert.Equal(t, "fast", config.GasPriceStrategy)
+	assert.Equal(t, float64(1.1), config.GasPriceMultiplier)
+	assert.Equal(t, float64(1.5), config.MaxGasPriceIncrement)
+	assert.Equal(t, 1*time.Second, config.MonitorInterval)
+	assert.Equal(t, 1*time.Minute, config.CleanupInterval)
+}
+
+func TestExecutor_MultipleOpportunities(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:       logger,
+		currentNonce: 10,
+		nonceCache:   make(map[uint64]*PendingTransaction),
+	}
+
+	// Track multiple opportunities
+	for i := 0; i < 5; i++ {
+		hash := common.HexToHash(string(rune(i)))
+		nonce := executor.getNextNonce()
+		opp := &arbitrage.Opportunity{
+			ID: string(rune(i)),
+		}
+
+		executor.trackPendingTransaction(nonce, hash, opp)
+	}
+
+	// Check all are tracked
+	assert.Len(t, executor.nonceCache, 5)
+	assert.Equal(t, uint64(15), executor.currentNonce)
+
+	// Get pending transactions
+	pending := executor.GetPendingTransactions()
+	assert.Len(t, pending, 5)
+}
+
+func TestExecutor_CleanupOldTransactions(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:     logger,
+		nonceCache: make(map[uint64]*PendingTransaction),
+	}
+
+	// Add old confirmed transaction
+	oldTime := time.Now().Add(-2 * time.Hour)
+	executor.nonceCache[1] = &PendingTransaction{
+		Hash:        common.HexToHash("0x01"),
+		Confirmed:   true,
+		LastChecked: oldTime,
+	}
+
+	// Add recent transaction
+	executor.nonceCache[2] = &PendingTransaction{
+		Hash:        common.HexToHash("0x02"),
+		Confirmed:   false,
+		LastChecked: time.Now(),
+	}
+
+	// Simulate cleanup (cutoff = 1 hour)
+	cutoff := time.Now().Add(-1 * time.Hour)
+	for nonce, pending := range executor.nonceCache {
+		if (pending.Confirmed || pending.Failed) && pending.LastChecked.Before(cutoff) {
+			delete(executor.nonceCache, nonce)
+		}
+	}
+
+	// Only recent transaction should remain
+	assert.Len(t, executor.nonceCache, 1)
+	_, exists := executor.nonceCache[2]
+	assert.True(t, exists)
+}
+
+// Benchmark tests
+func BenchmarkExecutor_getNextNonce(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:       logger,
+		currentNonce: 0,
+		nonceCache:   make(map[uint64]*PendingTransaction),
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = executor.getNextNonce()
+	}
+}
+
+func BenchmarkExecutor_trackPendingTransaction(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:     logger,
+		nonceCache: make(map[uint64]*PendingTransaction),
+	}
+
+	hash := common.HexToHash("0x123")
+	opp := &arbitrage.Opportunity{
+		ID: "test-opp",
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		executor.trackPendingTransaction(uint64(i), hash, opp)
+	}
+}
+
+func BenchmarkExecutor_GetPendingTransactions(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	executor := &Executor{
+		logger:     logger,
+		nonceCache: make(map[uint64]*PendingTransaction),
+	}
+
+	// Add 100 pending transactions
+	for i := 0; i < 100; i++ {
+		executor.nonceCache[uint64(i)] = &PendingTransaction{
+			Hash:      common.HexToHash(string(rune(i))),
+			Confirmed: false,
+			Failed:    false,
+		}
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = executor.GetPendingTransactions()
+	}
+}
diff --git a/pkg/execution/flashloan_test.go b/pkg/execution/flashloan_test.go
new file mode 100644
index 0000000..0b83222
--- /dev/null
+++ b/pkg/execution/flashloan_test.go
@@ -0,0 +1,482 @@
+package execution
+
+import (
+	"context"
+	"log/slog"
+	"math/big"
+	"os"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/your-org/mev-bot/pkg/arbitrage"
+)
+
+func TestNewFlashloanManager(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewFlashloanManager(nil, logger)
+
+	assert.NotNil(t, manager)
+	assert.NotNil(t, manager.config)
+	assert.NotNil(t, manager.aaveV3Encoder)
+	assert.NotNil(t, manager.uniswapV3Encoder)
+	assert.NotNil(t, manager.uniswapV2Encoder)
+}
+
+func TestDefaultFlashloanConfig(t *testing.T) {
+	config := DefaultFlashloanConfig()
+
+	assert.NotNil(t, config)
+	assert.Len(t, config.PreferredProviders, 3)
+	assert.Equal(t, FlashloanProviderAaveV3, config.PreferredProviders[0])
+	assert.Equal(t, uint16(9), config.AaveV3FeeBPS)
+	assert.Equal(t, uint16(0), config.UniswapV3FeeBPS)
+	assert.Equal(t, uint16(30), config.UniswapV2FeeBPS)
+}
+
+func TestFlashloanManager_BuildFlashloanTransaction_AaveV3(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultFlashloanConfig()
+	config.ExecutorContract = common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	manager := NewFlashloanManager(config, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+	}
+
+	swapCalldata := []byte{0x01, 0x02, 0x03, 0x04}
+
+	tx, err := manager.BuildFlashloanTransaction(context.Background(), opp, swapCalldata)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.Equal(t, FlashloanProviderAaveV3, tx.Provider)
+	assert.NotEmpty(t, tx.To)
+	assert.NotEmpty(t, tx.Data)
+	assert.NotNil(t, tx.Fee)
+	assert.True(t, tx.Fee.Cmp(big.NewInt(0)) > 0) // Fee should be > 0
+}
+
+func TestFlashloanManager_BuildFlashloanTransaction_UniswapV3(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultFlashloanConfig()
+	config.ExecutorContract = common.HexToAddress("0x0000000000000000000000000000000000000001")
+	config.PreferredProviders = []FlashloanProvider{FlashloanProviderUniswapV3}
+
+	manager := NewFlashloanManager(config, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+	}
+
+	swapCalldata := []byte{0x01, 0x02, 0x03, 0x04}
+
+	tx, err := manager.BuildFlashloanTransaction(context.Background(), opp, swapCalldata)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.Equal(t, FlashloanProviderUniswapV3, tx.Provider)
+	assert.NotEmpty(t, tx.To)
+	assert.NotEmpty(t, tx.Data)
+	assert.Equal(t, big.NewInt(0), tx.Fee) // UniswapV3 has no separate fee
+}
+
+func TestFlashloanManager_BuildFlashloanTransaction_UniswapV2(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultFlashloanConfig()
+	config.ExecutorContract = common.HexToAddress("0x0000000000000000000000000000000000000001")
+	config.PreferredProviders = []FlashloanProvider{FlashloanProviderUniswapV2}
+
+	manager := NewFlashloanManager(config, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+	}
+
+	swapCalldata := []byte{0x01, 0x02, 0x03, 0x04}
+
+	tx, err := manager.BuildFlashloanTransaction(context.Background(), opp, swapCalldata)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.Equal(t, FlashloanProviderUniswapV2, tx.Provider)
+	assert.NotEmpty(t, tx.To)
+	assert.NotEmpty(t, tx.Data)
+	assert.True(t, tx.Fee.Cmp(big.NewInt(0)) > 0) // Fee should be > 0
+}
+
+func TestFlashloanManager_selectProvider_NoProviders(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := &FlashloanConfig{
+		PreferredProviders: []FlashloanProvider{},
+	}
+
+	manager := NewFlashloanManager(config, logger)
+
+	token := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	amount := big.NewInt(1e18)
+
+	_, err := manager.selectProvider(context.Background(), token, amount)
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "no flashloan providers configured")
+}
+
+func TestFlashloanManager_calculateFee(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewFlashloanManager(nil, logger)
+
+	tests := []struct {
+		name        string
+		amount      *big.Int
+		feeBPS      uint16
+		expectedFee *big.Int
+	}{
+		{
+			name:        "Aave V3 fee (9 bps)",
+			amount:      big.NewInt(1e18),
+			feeBPS:      9,
+			expectedFee: big.NewInt(9e14), // 0.0009 * 1e18
+		},
+		{
+			name:        "Uniswap V2 fee (30 bps)",
+			amount:      big.NewInt(1e18),
+			feeBPS:      30,
+			expectedFee: big.NewInt(3e15), // 0.003 * 1e18
+		},
+		{
+			name:        "Zero fee",
+			amount:      big.NewInt(1e18),
+			feeBPS:      0,
+			expectedFee: big.NewInt(0),
+		},
+		{
+			name:        "Small amount",
+			amount:      big.NewInt(1000),
+			feeBPS:      9,
+			expectedFee: big.NewInt(0), // Rounds down to 0
+		},
+		{
+			name:        "Large amount",
+			amount:      big.NewInt(1000e18),
+			feeBPS:      9,
+			expectedFee: big.NewInt(9e20), // 0.0009 * 1000e18
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			fee := manager.calculateFee(tt.amount, tt.feeBPS)
+			assert.Equal(t, tt.expectedFee, fee)
+		})
+	}
+}
+
+func TestFlashloanManager_CalculateTotalCost(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewFlashloanManager(nil, logger)
+
+	tests := []struct {
+		name          string
+		amount        *big.Int
+		feeBPS        uint16
+		expectedTotal *big.Int
+	}{
+		{
+			name:          "Aave V3 cost",
+			amount:        big.NewInt(1e18),
+			feeBPS:        9,
+			expectedTotal: big.NewInt(1.0009e18),
+		},
+		{
+			name:          "Uniswap V2 cost",
+			amount:        big.NewInt(1e18),
+			feeBPS:        30,
+			expectedTotal: big.NewInt(1.003e18),
+		},
+		{
+			name:          "Zero fee cost",
+			amount:        big.NewInt(1e18),
+			feeBPS:        0,
+			expectedTotal: big.NewInt(1e18),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			total := manager.CalculateTotalCost(tt.amount, tt.feeBPS)
+			assert.Equal(t, tt.expectedTotal, total)
+		})
+	}
+}
+
+func TestAaveV3FlashloanEncoder_EncodeFlashloan(t *testing.T) {
+	encoder := NewAaveV3FlashloanEncoder()
+
+	assets := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+	}
+	amounts := []*big.Int{
+		big.NewInt(1e18),
+	}
+	receiverAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	params := []byte{0x01, 0x02, 0x03, 0x04}
+
+	to, data, err := encoder.EncodeFlashloan(assets, amounts, receiverAddress, params)
+
+	require.NoError(t, err)
+	assert.Equal(t, AaveV3PoolAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID
+	// flashLoan(address,address[],uint256[],uint256[],address,bytes,uint16)
+	assert.GreaterOrEqual(t, len(data), 4)
+}
+
+func TestAaveV3FlashloanEncoder_EncodeFlashloan_MultipleAssets(t *testing.T) {
+	encoder := NewAaveV3FlashloanEncoder()
+
+	assets := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+	}
+	amounts := []*big.Int{
+		big.NewInt(1e18),
+		big.NewInt(1500e6),
+	}
+	receiverAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	params := []byte{0x01, 0x02, 0x03, 0x04}
+
+	to, data, err := encoder.EncodeFlashloan(assets, amounts, receiverAddress, params)
+
+	require.NoError(t, err)
+	assert.Equal(t, AaveV3PoolAddress, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestAaveV3FlashloanEncoder_EncodeFlashloan_EmptyParams(t *testing.T) {
+	encoder := NewAaveV3FlashloanEncoder()
+
+	assets := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+	}
+	amounts := []*big.Int{
+		big.NewInt(1e18),
+	}
+	receiverAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	params := []byte{}
+
+	to, data, err := encoder.EncodeFlashloan(assets, amounts, receiverAddress, params)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV3FlashloanEncoder_EncodeFlash(t *testing.T) {
+	encoder := NewUniswapV3FlashloanEncoder()
+
+	token := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	amount := big.NewInt(1e18)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	data := []byte{0x01, 0x02, 0x03, 0x04}
+
+	to, calldata, err := encoder.EncodeFlash(token, amount, poolAddress, recipient, data)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, calldata)
+
+	// Check method ID
+	// flash(address,uint256,uint256,bytes)
+	assert.GreaterOrEqual(t, len(calldata), 4)
+}
+
+func TestUniswapV3FlashloanEncoder_EncodeFlash_EmptyData(t *testing.T) {
+	encoder := NewUniswapV3FlashloanEncoder()
+
+	token := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	amount := big.NewInt(1e18)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	data := []byte{}
+
+	to, calldata, err := encoder.EncodeFlash(token, amount, poolAddress, recipient, data)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, calldata)
+}
+
+func TestUniswapV2FlashloanEncoder_EncodeFlash(t *testing.T) {
+	encoder := NewUniswapV2FlashloanEncoder()
+
+	token := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	amount := big.NewInt(1e18)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	data := []byte{0x01, 0x02, 0x03, 0x04}
+
+	to, calldata, err := encoder.EncodeFlash(token, amount, poolAddress, recipient, data)
+
+	require.NoError(t, err)
+	assert.Equal(t, poolAddress, to)
+	assert.NotEmpty(t, calldata)
+
+	// Check method ID
+	// swap(uint256,uint256,address,bytes)
+	assert.GreaterOrEqual(t, len(calldata), 4)
+}
+
+func TestUniswapV2FlashloanEncoder_EncodeFlash_EmptyData(t *testing.T) {
+	encoder := NewUniswapV2FlashloanEncoder()
+
+	token := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	amount := big.NewInt(1e18)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	data := []byte{}
+
+	to, calldata, err := encoder.EncodeFlash(token, amount, poolAddress, recipient, data)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, calldata)
+}
+
+func TestFlashloanManager_ZeroAmount(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultFlashloanConfig()
+	config.ExecutorContract = common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	manager := NewFlashloanManager(config, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(0),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+	}
+
+	swapCalldata := []byte{0x01, 0x02, 0x03, 0x04}
+
+	tx, err := manager.BuildFlashloanTransaction(context.Background(), opp, swapCalldata)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.Equal(t, big.NewInt(0), tx.Fee) // Fee should be 0 for 0 amount
+}
+
+func TestFlashloanManager_LargeAmount(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultFlashloanConfig()
+	config.ExecutorContract = common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	manager := NewFlashloanManager(config, logger)
+
+	// 1000 ETH
+	largeAmount := new(big.Int).Mul(big.NewInt(1000), big.NewInt(1e18))
+
+	opp := &arbitrage.Opportunity{
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: largeAmount,
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+	}
+
+	swapCalldata := []byte{0x01, 0x02, 0x03, 0x04}
+
+	tx, err := manager.BuildFlashloanTransaction(context.Background(), opp, swapCalldata)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.True(t, tx.Fee.Cmp(big.NewInt(0)) > 0)
+
+	// Verify fee is reasonable (0.09% of 1000 ETH = 0.9 ETH)
+	expectedFee := new(big.Int).Mul(big.NewInt(9e17), big.NewInt(1)) // 0.9 ETH
+	assert.Equal(t, expectedFee, tx.Fee)
+}
+
+// Benchmark tests
+func BenchmarkFlashloanManager_BuildFlashloanTransaction(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultFlashloanConfig()
+	config.ExecutorContract = common.HexToAddress("0x0000000000000000000000000000000000000001")
+
+	manager := NewFlashloanManager(config, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+	}
+
+	swapCalldata := []byte{0x01, 0x02, 0x03, 0x04}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = manager.BuildFlashloanTransaction(context.Background(), opp, swapCalldata)
+	}
+}
+
+func BenchmarkAaveV3FlashloanEncoder_EncodeFlashloan(b *testing.B) {
+	encoder := NewAaveV3FlashloanEncoder()
+
+	assets := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+	}
+	amounts := []*big.Int{
+		big.NewInt(1e18),
+	}
+	receiverAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	params := []byte{0x01, 0x02, 0x03, 0x04}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _, _ = encoder.EncodeFlashloan(assets, amounts, receiverAddress, params)
+	}
+}
diff --git a/pkg/execution/risk_manager_test.go b/pkg/execution/risk_manager_test.go
new file mode 100644
index 0000000..08ed0f0
--- /dev/null
+++ b/pkg/execution/risk_manager_test.go
@@ -0,0 +1,633 @@
+package execution
+
+import (
+	"context"
+	"log/slog"
+	"math/big"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/your-org/mev-bot/pkg/arbitrage"
+)
+
+func TestDefaultRiskManagerConfig(t *testing.T) {
+	config := DefaultRiskManagerConfig()
+
+	assert.NotNil(t, config)
+	assert.True(t, config.Enabled)
+	assert.NotNil(t, config.MaxPositionSize)
+	assert.NotNil(t, config.MaxDailyVolume)
+	assert.NotNil(t, config.MinProfitThreshold)
+	assert.Equal(t, float64(0.01), config.MinROI)
+	assert.Equal(t, uint16(200), config.MaxSlippageBPS)
+	assert.Equal(t, uint64(5), config.MaxConcurrentTxs)
+}
+
+func TestNewRiskManager(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	assert.NotNil(t, manager)
+	assert.NotNil(t, manager.config)
+	assert.NotNil(t, manager.activeTxs)
+	assert.NotNil(t, manager.dailyVolume)
+	assert.NotNil(t, manager.recentFailures)
+	assert.False(t, manager.circuitBreakerOpen)
+}
+
+func TestRiskManager_AssessRisk_Success(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false // Disable simulation for unit test
+
+	manager := NewRiskManager(config, nil, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1, // 10%
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9), // 50 gwei
+		MaxPriorityFeePerGas: big.NewInt(2e9),  // 2 gwei
+		GasLimit:             180000,
+		Slippage:             50, // 0.5%
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.NotNil(t, assessment)
+	assert.True(t, assessment.Approved)
+	assert.Empty(t, assessment.Warnings)
+}
+
+func TestRiskManager_AssessRisk_CircuitBreakerOpen(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Open circuit breaker
+	manager.openCircuitBreaker()
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "circuit breaker")
+}
+
+func TestRiskManager_AssessRisk_PositionSizeExceeded(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Create opportunity with amount exceeding max position size
+	largeAmount := new(big.Int).Add(config.MaxPositionSize, big.NewInt(1))
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  largeAmount,
+		OutputAmount: new(big.Int).Mul(largeAmount, big.NewInt(11)),
+		NetProfit:    big.NewInt(1e18),
+		ROI:          0.1,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "position size")
+}
+
+func TestRiskManager_AssessRisk_DailyVolumeExceeded(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Set daily volume to max
+	manager.dailyVolume = config.MaxDailyVolume
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "daily volume")
+}
+
+func TestRiskManager_AssessRisk_GasPriceTooHigh(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1,
+		EstimatedGas: 150000,
+	}
+
+	// Set gas price above max
+	tx := &SwapTransaction{
+		MaxFeePerGas:         new(big.Int).Add(config.MaxGasPrice, big.NewInt(1)),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "gas price")
+}
+
+func TestRiskManager_AssessRisk_ProfitTooLow(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Profit below threshold
+	lowProfit := new(big.Int).Sub(config.MinProfitThreshold, big.NewInt(1))
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: new(big.Int).Add(big.NewInt(1e18), lowProfit),
+		NetProfit:    lowProfit,
+		ROI:          0.00001,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "profit")
+}
+
+func TestRiskManager_AssessRisk_ROITooLow(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.005e18),
+		NetProfit:    big.NewInt(0.005e18), // 0.5% ROI, below 1% threshold
+		ROI:          0.005,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "ROI")
+}
+
+func TestRiskManager_AssessRisk_SlippageTooHigh(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             300, // 3%, above 2% max
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "slippage")
+}
+
+func TestRiskManager_AssessRisk_ConcurrentLimitExceeded(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+	config.MaxConcurrentTxs = 2
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Add max concurrent transactions
+	manager.activeTxs[common.HexToHash("0x01")] = &ActiveTransaction{}
+	manager.activeTxs[common.HexToHash("0x02")] = &ActiveTransaction{}
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.False(t, assessment.Approved)
+	assert.Contains(t, assessment.Reason, "concurrent")
+}
+
+func TestRiskManager_TrackTransaction(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	hash := common.HexToHash("0x123")
+	opp := &arbitrage.Opportunity{
+		InputAmount: big.NewInt(1e18),
+		NetProfit:   big.NewInt(0.1e18),
+	}
+	gasPrice := big.NewInt(50e9)
+
+	manager.TrackTransaction(hash, opp, gasPrice)
+
+	// Check transaction is tracked
+	manager.mu.RLock()
+	tx, exists := manager.activeTxs[hash]
+	manager.mu.RUnlock()
+
+	assert.True(t, exists)
+	assert.NotNil(t, tx)
+	assert.Equal(t, hash, tx.Hash)
+	assert.Equal(t, opp.InputAmount, tx.Amount)
+	assert.Equal(t, gasPrice, tx.GasPrice)
+}
+
+func TestRiskManager_UntrackTransaction(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	hash := common.HexToHash("0x123")
+	manager.activeTxs[hash] = &ActiveTransaction{Hash: hash}
+
+	manager.UntrackTransaction(hash)
+
+	// Check transaction is no longer tracked
+	manager.mu.RLock()
+	_, exists := manager.activeTxs[hash]
+	manager.mu.RUnlock()
+
+	assert.False(t, exists)
+}
+
+func TestRiskManager_RecordFailure(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.CircuitBreakerFailures = 3
+	config.CircuitBreakerWindow = 1 * time.Minute
+
+	manager := NewRiskManager(config, nil, logger)
+
+	hash := common.HexToHash("0x123")
+
+	// Record failures below threshold
+	manager.RecordFailure(hash, "test failure 1")
+	assert.False(t, manager.circuitBreakerOpen)
+
+	manager.RecordFailure(hash, "test failure 2")
+	assert.False(t, manager.circuitBreakerOpen)
+
+	// Third failure should open circuit breaker
+	manager.RecordFailure(hash, "test failure 3")
+	assert.True(t, manager.circuitBreakerOpen)
+}
+
+func TestRiskManager_RecordSuccess(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	hash := common.HexToHash("0x123")
+	actualProfit := big.NewInt(0.1e18)
+
+	manager.RecordSuccess(hash, actualProfit)
+
+	// Check that recent failures were cleared
+	assert.Empty(t, manager.recentFailures)
+}
+
+func TestRiskManager_CircuitBreaker_Cooldown(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.CircuitBreakerCooldown = 1 * time.Millisecond
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Open circuit breaker
+	manager.openCircuitBreaker()
+	assert.True(t, manager.circuitBreakerOpen)
+
+	// Wait for cooldown
+	time.Sleep(2 * time.Millisecond)
+
+	// Circuit breaker should be closed after cooldown
+	assert.False(t, manager.checkCircuitBreaker())
+}
+
+func TestRiskManager_checkConcurrentLimit(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MaxConcurrentTxs = 3
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Add transactions below limit
+	manager.activeTxs[common.HexToHash("0x01")] = &ActiveTransaction{}
+	manager.activeTxs[common.HexToHash("0x02")] = &ActiveTransaction{}
+
+	assert.True(t, manager.checkConcurrentLimit())
+
+	// Add transaction at limit
+	manager.activeTxs[common.HexToHash("0x03")] = &ActiveTransaction{}
+
+	assert.False(t, manager.checkConcurrentLimit())
+}
+
+func TestRiskManager_checkPositionSize(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MaxPositionSize = big.NewInt(10e18)
+
+	manager := NewRiskManager(config, nil, logger)
+
+	assert.True(t, manager.checkPositionSize(big.NewInt(5e18)))
+	assert.True(t, manager.checkPositionSize(big.NewInt(10e18)))
+	assert.False(t, manager.checkPositionSize(big.NewInt(11e18)))
+}
+
+func TestRiskManager_checkDailyVolume(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MaxDailyVolume = big.NewInt(100e18)
+
+	manager := NewRiskManager(config, nil, logger)
+	manager.dailyVolume = big.NewInt(90e18)
+
+	assert.True(t, manager.checkDailyVolume(big.NewInt(5e18)))
+	assert.True(t, manager.checkDailyVolume(big.NewInt(10e18)))
+	assert.False(t, manager.checkDailyVolume(big.NewInt(15e18)))
+}
+
+func TestRiskManager_updateDailyVolume(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	initialVolume := big.NewInt(10e18)
+	manager.dailyVolume = initialVolume
+
+	addAmount := big.NewInt(5e18)
+	manager.updateDailyVolume(addAmount)
+
+	expectedVolume := new(big.Int).Add(initialVolume, addAmount)
+	assert.Equal(t, expectedVolume, manager.dailyVolume)
+}
+
+func TestRiskManager_checkGasPrice(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MaxGasPrice = big.NewInt(100e9) // 100 gwei
+
+	manager := NewRiskManager(config, nil, logger)
+
+	assert.True(t, manager.checkGasPrice(big.NewInt(50e9)))
+	assert.True(t, manager.checkGasPrice(big.NewInt(100e9)))
+	assert.False(t, manager.checkGasPrice(big.NewInt(101e9)))
+}
+
+func TestRiskManager_checkGasCost(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MaxGasCost = big.NewInt(0.1e18) // 0.1 ETH
+
+	manager := NewRiskManager(config, nil, logger)
+
+	assert.True(t, manager.checkGasCost(big.NewInt(0.05e18)))
+	assert.True(t, manager.checkGasCost(big.NewInt(0.1e18)))
+	assert.False(t, manager.checkGasCost(big.NewInt(0.11e18)))
+}
+
+func TestRiskManager_checkMinProfit(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MinProfitThreshold = big.NewInt(0.01e18) // 0.01 ETH
+
+	manager := NewRiskManager(config, nil, logger)
+
+	assert.False(t, manager.checkMinProfit(big.NewInt(0.005e18)))
+	assert.True(t, manager.checkMinProfit(big.NewInt(0.01e18)))
+	assert.True(t, manager.checkMinProfit(big.NewInt(0.02e18)))
+}
+
+func TestRiskManager_checkMinROI(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MinROI = 0.01 // 1%
+
+	manager := NewRiskManager(config, nil, logger)
+
+	assert.False(t, manager.checkMinROI(0.005)) // 0.5%
+	assert.True(t, manager.checkMinROI(0.01))   // 1%
+	assert.True(t, manager.checkMinROI(0.02))   // 2%
+}
+
+func TestRiskManager_checkSlippage(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.MaxSlippageBPS = 200 // 2%
+
+	manager := NewRiskManager(config, nil, logger)
+
+	assert.True(t, manager.checkSlippage(100))  // 1%
+	assert.True(t, manager.checkSlippage(200))  // 2%
+	assert.False(t, manager.checkSlippage(300)) // 3%
+}
+
+func TestRiskManager_GetActiveTransactions(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	// Add some active transactions
+	manager.activeTxs[common.HexToHash("0x01")] = &ActiveTransaction{Hash: common.HexToHash("0x01")}
+	manager.activeTxs[common.HexToHash("0x02")] = &ActiveTransaction{Hash: common.HexToHash("0x02")}
+
+	activeTxs := manager.GetActiveTransactions()
+
+	assert.Len(t, activeTxs, 2)
+}
+
+func TestRiskManager_GetStats(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	// Add some state
+	manager.activeTxs[common.HexToHash("0x01")] = &ActiveTransaction{}
+	manager.dailyVolume = big.NewInt(50e18)
+	manager.circuitBreakerOpen = true
+
+	stats := manager.GetStats()
+
+	assert.NotNil(t, stats)
+	assert.Equal(t, 1, stats["active_transactions"])
+	assert.Equal(t, "50000000000000000000", stats["daily_volume"])
+	assert.Equal(t, true, stats["circuit_breaker_open"])
+}
+
+func TestRiskManager_AssessRisk_WithWarnings(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	// Create opportunity with high gas cost (should generate warning)
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1,
+		EstimatedGas: 2000000, // Very high gas
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             2400000,
+		Slippage:             50,
+	}
+
+	assessment, err := manager.AssessRisk(context.Background(), opp, tx)
+
+	require.NoError(t, err)
+	assert.True(t, assessment.Approved) // Should still be approved
+	assert.NotEmpty(t, assessment.Warnings) // But with warnings
+}
+
+// Benchmark tests
+func BenchmarkRiskManager_AssessRisk(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	config := DefaultRiskManagerConfig()
+	config.SimulationEnabled = false
+
+	manager := NewRiskManager(config, nil, logger)
+
+	opp := &arbitrage.Opportunity{
+		InputAmount:  big.NewInt(1e18),
+		OutputAmount: big.NewInt(1.1e18),
+		NetProfit:    big.NewInt(0.1e18),
+		ROI:          0.1,
+		EstimatedGas: 150000,
+	}
+
+	tx := &SwapTransaction{
+		MaxFeePerGas:         big.NewInt(50e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+		GasLimit:             180000,
+		Slippage:             50,
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = manager.AssessRisk(context.Background(), opp, tx)
+	}
+}
+
+func BenchmarkRiskManager_checkCircuitBreaker(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	manager := NewRiskManager(nil, nil, logger)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = manager.checkCircuitBreaker()
+	}
+}
diff --git a/pkg/execution/transaction_builder_test.go b/pkg/execution/transaction_builder_test.go
new file mode 100644
index 0000000..b019665
--- /dev/null
+++ b/pkg/execution/transaction_builder_test.go
@@ -0,0 +1,560 @@
+package execution
+
+import (
+	"context"
+	"log/slog"
+	"math/big"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/your-org/mev-bot/pkg/arbitrage"
+	mevtypes "github.com/your-org/mev-bot/pkg/types"
+)
+
+func TestDefaultTransactionBuilderConfig(t *testing.T) {
+	config := DefaultTransactionBuilderConfig()
+
+	assert.NotNil(t, config)
+	assert.Equal(t, uint16(50), config.DefaultSlippageBPS)
+	assert.Equal(t, uint16(300), config.MaxSlippageBPS)
+	assert.Equal(t, float64(1.2), config.GasLimitMultiplier)
+	assert.Equal(t, uint64(3000000), config.MaxGasLimit)
+	assert.Equal(t, 5*time.Minute, config.DefaultDeadline)
+}
+
+func TestNewTransactionBuilder(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161) // Arbitrum
+
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	assert.NotNil(t, builder)
+	assert.NotNil(t, builder.config)
+	assert.Equal(t, chainID, builder.chainID)
+	assert.NotNil(t, builder.uniswapV2Encoder)
+	assert.NotNil(t, builder.uniswapV3Encoder)
+	assert.NotNil(t, builder.curveEncoder)
+}
+
+func TestTransactionBuilder_BuildTransaction_SingleSwap_UniswapV2(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-1",
+		Type:        arbitrage.OpportunityTypeTwoPool,
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		OutputToken: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+		OutputAmount: big.NewInt(1500e6),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolUniswapV2,
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(1e18),
+				AmountOut:   big.NewInt(1500e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+		},
+		EstimatedGas: 150000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	tx, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.NotEmpty(t, tx.To)
+	assert.NotEmpty(t, tx.Data)
+	assert.NotNil(t, tx.Value)
+	assert.Greater(t, tx.GasLimit, uint64(0))
+	assert.NotNil(t, tx.MaxFeePerGas)
+	assert.NotNil(t, tx.MaxPriorityFeePerGas)
+	assert.NotNil(t, tx.MinOutput)
+	assert.False(t, tx.RequiresFlashloan)
+	assert.Equal(t, uint16(50), tx.Slippage) // Default slippage
+}
+
+func TestTransactionBuilder_BuildTransaction_SingleSwap_UniswapV3(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-2",
+		Type:        arbitrage.OpportunityTypeTwoPool,
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		OutputToken: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+		OutputAmount: big.NewInt(1500e6),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolUniswapV3,
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(1e18),
+				AmountOut:   big.NewInt(1500e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+				Fee:         3000, // 0.3%
+			},
+		},
+		EstimatedGas: 150000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	tx, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.NotEmpty(t, tx.To)
+	assert.NotEmpty(t, tx.Data)
+	assert.Equal(t, UniswapV3SwapRouterAddress, tx.To)
+}
+
+func TestTransactionBuilder_BuildTransaction_MultiHop_UniswapV2(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-3",
+		Type:        arbitrage.OpportunityTypeMultiHop,
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		OutputToken: common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+		OutputAmount: big.NewInt(1e7),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolUniswapV2,
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(1e18),
+				AmountOut:   big.NewInt(1500e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+			{
+				Protocol:    mevtypes.ProtocolUniswapV2,
+				TokenIn:     common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				TokenOut:    common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+				AmountIn:    big.NewInt(1500e6),
+				AmountOut:   big.NewInt(1e7),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+		EstimatedGas: 250000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	tx, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.NotEmpty(t, tx.To)
+	assert.NotEmpty(t, tx.Data)
+	assert.Equal(t, UniswapV2RouterAddress, tx.To)
+}
+
+func TestTransactionBuilder_BuildTransaction_MultiHop_UniswapV3(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-4",
+		Type:        arbitrage.OpportunityTypeMultiHop,
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		OutputToken: common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+		OutputAmount: big.NewInt(1e7),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolUniswapV3,
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(1e18),
+				AmountOut:   big.NewInt(1500e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+				Fee:         3000,
+			},
+			{
+				Protocol:    mevtypes.ProtocolUniswapV3,
+				TokenIn:     common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				TokenOut:    common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+				AmountIn:    big.NewInt(1500e6),
+				AmountOut:   big.NewInt(1e7),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+				Fee:         500,
+			},
+		},
+		EstimatedGas: 250000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	tx, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	assert.Equal(t, UniswapV3SwapRouterAddress, tx.To)
+}
+
+func TestTransactionBuilder_BuildTransaction_Curve(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-5",
+		Type:        arbitrage.OpportunityTypeTwoPool,
+		InputToken:  common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+		InputAmount: big.NewInt(1500e6),
+		OutputToken: common.HexToAddress("0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9"),
+		OutputAmount: big.NewInt(1500e6),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolCurve,
+				TokenIn:     common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				TokenOut:    common.HexToAddress("0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9"),
+				AmountIn:    big.NewInt(1500e6),
+				AmountOut:   big.NewInt(1500e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+		},
+		EstimatedGas: 200000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	tx, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	require.NoError(t, err)
+	assert.NotNil(t, tx)
+	// For Curve, tx.To should be the pool address
+	assert.Equal(t, opp.Path[0].PoolAddress, tx.To)
+}
+
+func TestTransactionBuilder_BuildTransaction_EmptyPath(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-6",
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		Path:        []arbitrage.SwapStep{},
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	_, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "empty swap path")
+}
+
+func TestTransactionBuilder_BuildTransaction_UnsupportedProtocol(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-7",
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    "unknown_protocol",
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(1e18),
+				AmountOut:   big.NewInt(1500e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+		},
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	_, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unsupported protocol")
+}
+
+func TestTransactionBuilder_calculateMinOutput(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	tests := []struct {
+		name           string
+		outputAmount   *big.Int
+		slippageBPS    uint16
+		expectedMin    *big.Int
+	}{
+		{
+			name:         "0.5% slippage",
+			outputAmount: big.NewInt(1000e6),
+			slippageBPS:  50,
+			expectedMin:  big.NewInt(995e6), // 0.5% less
+		},
+		{
+			name:         "1% slippage",
+			outputAmount: big.NewInt(1000e6),
+			slippageBPS:  100,
+			expectedMin:  big.NewInt(990e6), // 1% less
+		},
+		{
+			name:         "3% slippage",
+			outputAmount: big.NewInt(1000e6),
+			slippageBPS:  300,
+			expectedMin:  big.NewInt(970e6), // 3% less
+		},
+		{
+			name:         "Zero slippage",
+			outputAmount: big.NewInt(1000e6),
+			slippageBPS:  0,
+			expectedMin:  big.NewInt(1000e6), // No change
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			minOutput := builder.calculateMinOutput(tt.outputAmount, tt.slippageBPS)
+			assert.Equal(t, tt.expectedMin, minOutput)
+		})
+	}
+}
+
+func TestTransactionBuilder_calculateGasLimit(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	tests := []struct {
+		name         string
+		estimatedGas uint64
+		expectedMin  uint64
+		expectedMax  uint64
+	}{
+		{
+			name:         "Normal gas estimate",
+			estimatedGas: 150000,
+			expectedMin:  180000, // 150k * 1.2
+			expectedMax:  180001,
+		},
+		{
+			name:         "High gas estimate",
+			estimatedGas: 2500000,
+			expectedMin:  3000000, // Capped at max
+			expectedMax:  3000000,
+		},
+		{
+			name:         "Zero gas estimate",
+			estimatedGas: 0,
+			expectedMin:  0, // 0 * 1.2
+			expectedMax:  0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gasLimit := builder.calculateGasLimit(tt.estimatedGas)
+			assert.GreaterOrEqual(t, gasLimit, tt.expectedMin)
+			assert.LessOrEqual(t, gasLimit, tt.expectedMax)
+		})
+	}
+}
+
+func TestTransactionBuilder_SignTransaction(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	// Create a test private key
+	privateKey, err := crypto.GenerateKey()
+	require.NoError(t, err)
+
+	tx := &SwapTransaction{
+		To:                   common.HexToAddress("0x0000000000000000000000000000000000000001"),
+		Data:                 []byte{0x01, 0x02, 0x03, 0x04},
+		Value:                big.NewInt(0),
+		GasLimit:             180000,
+		MaxFeePerGas:         big.NewInt(100e9), // 100 gwei
+		MaxPriorityFeePerGas: big.NewInt(2e9),   // 2 gwei
+	}
+
+	nonce := uint64(5)
+
+	signedTx, err := builder.SignTransaction(tx, nonce, crypto.FromECDSA(privateKey))
+
+	require.NoError(t, err)
+	assert.NotNil(t, signedTx)
+	assert.Equal(t, nonce, signedTx.Nonce())
+	assert.Equal(t, tx.To, *signedTx.To())
+	assert.Equal(t, tx.GasLimit, signedTx.Gas())
+	assert.Equal(t, tx.MaxFeePerGas, signedTx.GasFeeCap())
+	assert.Equal(t, tx.MaxPriorityFeePerGas, signedTx.GasTipCap())
+}
+
+func TestTransactionBuilder_SignTransaction_InvalidKey(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	tx := &SwapTransaction{
+		To:                   common.HexToAddress("0x0000000000000000000000000000000000000001"),
+		Data:                 []byte{0x01, 0x02, 0x03, 0x04},
+		Value:                big.NewInt(0),
+		GasLimit:             180000,
+		MaxFeePerGas:         big.NewInt(100e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+	}
+
+	nonce := uint64(5)
+	invalidKey := []byte{0x01, 0x02, 0x03} // Too short
+
+	_, err := builder.SignTransaction(tx, nonce, invalidKey)
+
+	assert.Error(t, err)
+}
+
+func TestTransactionBuilder_CustomSlippage(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+
+	config := DefaultTransactionBuilderConfig()
+	config.DefaultSlippageBPS = 100 // 1% slippage
+
+	builder := NewTransactionBuilder(config, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-8",
+		Type:        arbitrage.OpportunityTypeTwoPool,
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		OutputToken: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+		OutputAmount: big.NewInt(1000e6),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolUniswapV2,
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(1e18),
+				AmountOut:   big.NewInt(1000e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+		},
+		EstimatedGas: 150000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	tx, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	require.NoError(t, err)
+	assert.Equal(t, uint16(100), tx.Slippage)
+	// MinOutput should be 990e6 (1% slippage on 1000e6)
+	assert.Equal(t, big.NewInt(990e6), tx.MinOutput)
+}
+
+func TestTransactionBuilder_ZeroAmounts(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "test-opp-9",
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(0),
+		OutputToken: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+		OutputAmount: big.NewInt(0),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolUniswapV2,
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(0),
+				AmountOut:   big.NewInt(0),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+		},
+		EstimatedGas: 150000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	tx, err := builder.BuildTransaction(context.Background(), opp, fromAddress)
+
+	require.NoError(t, err)
+	assert.Equal(t, big.NewInt(0), tx.MinOutput)
+}
+
+// Benchmark tests
+func BenchmarkTransactionBuilder_BuildTransaction(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	opp := &arbitrage.Opportunity{
+		ID:          "bench-opp",
+		Type:        arbitrage.OpportunityTypeTwoPool,
+		InputToken:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+		InputAmount: big.NewInt(1e18),
+		OutputToken: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+		OutputAmount: big.NewInt(1500e6),
+		Path: []arbitrage.SwapStep{
+			{
+				Protocol:    mevtypes.ProtocolUniswapV2,
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				AmountIn:    big.NewInt(1e18),
+				AmountOut:   big.NewInt(1500e6),
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+		},
+		EstimatedGas: 150000,
+	}
+
+	fromAddress := common.HexToAddress("0x0000000000000000000000000000000000000002")
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = builder.BuildTransaction(context.Background(), opp, fromAddress)
+	}
+}
+
+func BenchmarkTransactionBuilder_SignTransaction(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+	chainID := big.NewInt(42161)
+	builder := NewTransactionBuilder(nil, chainID, logger)
+
+	privateKey, _ := crypto.GenerateKey()
+
+	tx := &SwapTransaction{
+		To:                   common.HexToAddress("0x0000000000000000000000000000000000000001"),
+		Data:                 []byte{0x01, 0x02, 0x03, 0x04},
+		Value:                big.NewInt(0),
+		GasLimit:             180000,
+		MaxFeePerGas:         big.NewInt(100e9),
+		MaxPriorityFeePerGas: big.NewInt(2e9),
+	}
+
+	nonce := uint64(5)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = builder.SignTransaction(tx, nonce, crypto.FromECDSA(privateKey))
+	}
+}
diff --git a/pkg/execution/uniswap_v2_encoder_test.go b/pkg/execution/uniswap_v2_encoder_test.go
new file mode 100644
index 0000000..64e15a3
--- /dev/null
+++ b/pkg/execution/uniswap_v2_encoder_test.go
@@ -0,0 +1,305 @@
+package execution
+
+import (
+	"math/big"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewUniswapV2Encoder(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+	assert.NotNil(t, encoder)
+	assert.Equal(t, UniswapV2RouterAddress, encoder.routerAddress)
+}
+
+func TestUniswapV2Encoder_EncodeSwap(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")  // WETH
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8") // USDC
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.routerAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID (first 4 bytes)
+	// swapExactTokensForTokens(uint256,uint256,address[],address,uint256)
+	assert.Len(t, data, 4+5*32+32+2*32) // methodID + 5 params + array length + 2 addresses
+
+	// Verify method signature
+	expectedMethodID := []byte{0x38, 0xed, 0x17, 0x39} // swapExactTokensForTokens signature
+	assert.Equal(t, expectedMethodID, data[:4])
+}
+
+func TestUniswapV2Encoder_EncodeMultiHopSwap(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	path := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"), // WETH
+		common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"), // USDC
+		common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"), // WBTC
+	}
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1e7)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeMultiHopSwap(
+		path,
+		amountIn,
+		minAmountOut,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.routerAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Verify method ID
+	expectedMethodID := []byte{0x38, 0xed, 0x17, 0x39}
+	assert.Equal(t, expectedMethodID, data[:4])
+}
+
+func TestUniswapV2Encoder_EncodeMultiHopSwap_EmptyPath(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	path := []common.Address{}
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1e7)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	_, _, err := encoder.EncodeMultiHopSwap(
+		path,
+		amountIn,
+		minAmountOut,
+		recipient,
+		deadline,
+	)
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "path must contain at least 2 tokens")
+}
+
+func TestUniswapV2Encoder_EncodeMultiHopSwap_SingleToken(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	path := []common.Address{
+		common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+	}
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1e7)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	_, _, err := encoder.EncodeMultiHopSwap(
+		path,
+		amountIn,
+		minAmountOut,
+		recipient,
+		deadline,
+	)
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "path must contain at least 2 tokens")
+}
+
+func TestUniswapV2Encoder_EncodeExactOutput(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountOut := big.NewInt(1500e6)
+	maxAmountIn := big.NewInt(2e18)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeExactOutput(
+		tokenIn,
+		tokenOut,
+		amountOut,
+		maxAmountIn,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.routerAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Verify method ID for swapTokensForExactTokens
+	assert.Len(t, data, 4+5*32+32+2*32)
+}
+
+func TestUniswapV2Encoder_ZeroAddresses(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	tokenIn := common.Address{}
+	tokenOut := common.Address{}
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.Address{}
+	recipient := common.Address{}
+	deadline := time.Now().Add(5 * time.Minute)
+
+	// Should not error with zero addresses (validation done elsewhere)
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV2Encoder_ZeroAmounts(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(0)
+	minAmountOut := big.NewInt(0)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	// Should not error with zero amounts (validation done elsewhere)
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV2Encoder_LargeAmounts(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+
+	// Max uint256
+	amountIn := new(big.Int)
+	amountIn.SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
+	minAmountOut := new(big.Int)
+	minAmountOut.SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
+
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV2Encoder_PastDeadline(t *testing.T) {
+	encoder := NewUniswapV2Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(-5 * time.Minute) // Past deadline
+
+	// Should not error (validation done on-chain)
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestPadLeft(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    []byte
+		length   int
+		expected int
+	}{
+		{
+			name:     "Empty input",
+			input:    []byte{},
+			length:   32,
+			expected: 32,
+		},
+		{
+			name:     "Small number",
+			input:    []byte{0x01},
+			length:   32,
+			expected: 32,
+		},
+		{
+			name:     "Full size",
+			input:    make([]byte, 32),
+			length:   32,
+			expected: 32,
+		},
+		{
+			name:     "Address",
+			input:    make([]byte, 20),
+			length:   32,
+			expected: 32,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := padLeft(tt.input, tt.length)
+			assert.Len(t, result, tt.expected)
+		})
+	}
+}
diff --git a/pkg/execution/uniswap_v3_encoder_test.go b/pkg/execution/uniswap_v3_encoder_test.go
new file mode 100644
index 0000000..b171419
--- /dev/null
+++ b/pkg/execution/uniswap_v3_encoder_test.go
@@ -0,0 +1,484 @@
+package execution
+
+import (
+	"math/big"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/your-org/mev-bot/pkg/arbitrage"
+	"github.com/your-org/mev-bot/pkg/cache"
+)
+
+func TestNewUniswapV3Encoder(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+	assert.NotNil(t, encoder)
+	assert.Equal(t, UniswapV3SwapRouterAddress, encoder.swapRouterAddress)
+}
+
+func TestUniswapV3Encoder_EncodeSwap(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")  // WETH
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8") // USDC
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	fee := uint32(3000) // 0.3%
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		fee,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.swapRouterAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Check method ID (first 4 bytes)
+	// exactInputSingle((address,address,uint24,address,uint256,uint256,uint256,uint160))
+	assert.GreaterOrEqual(t, len(data), 4)
+}
+
+func TestUniswapV3Encoder_EncodeMultiHopSwap(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	opp := &arbitrage.Opportunity{
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				Fee:         3000,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+			{
+				TokenIn:     common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				TokenOut:    common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+				Fee:         3000,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+		},
+	}
+
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000003")
+	minAmountOut := big.NewInt(1e7)
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeMultiHopSwap(
+		opp,
+		recipient,
+		minAmountOut,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.swapRouterAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Verify method ID for exactInput
+	assert.GreaterOrEqual(t, len(data), 4)
+}
+
+func TestUniswapV3Encoder_EncodeMultiHopSwap_SingleStep(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	opp := &arbitrage.Opportunity{
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				Fee:         3000,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+		},
+	}
+
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000003")
+	minAmountOut := big.NewInt(1500e6)
+	deadline := time.Now().Add(5 * time.Minute)
+
+	_, _, err := encoder.EncodeMultiHopSwap(
+		opp,
+		recipient,
+		minAmountOut,
+		deadline,
+	)
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "multi-hop requires at least 2 steps")
+}
+
+func TestUniswapV3Encoder_EncodeMultiHopSwap_EmptyPath(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	opp := &arbitrage.Opportunity{
+		InputAmount: big.NewInt(1e18),
+		Path:        []arbitrage.SwapStep{},
+	}
+
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000003")
+	minAmountOut := big.NewInt(1500e6)
+	deadline := time.Now().Add(5 * time.Minute)
+
+	_, _, err := encoder.EncodeMultiHopSwap(
+		opp,
+		recipient,
+		minAmountOut,
+		deadline,
+	)
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "multi-hop requires at least 2 steps")
+}
+
+func TestUniswapV3Encoder_buildEncodedPath(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	opp := &arbitrage.Opportunity{
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				Fee:      3000,
+			},
+			{
+				TokenIn:  common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				TokenOut: common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+				Fee:      500,
+			},
+		},
+	}
+
+	path := encoder.buildEncodedPath(opp)
+
+	// Path should be: token (20) + fee (3) + token (20) + fee (3) + token (20) = 66 bytes
+	assert.Len(t, path, 66)
+
+	// First 20 bytes should be first token
+	assert.Equal(t, opp.Path[0].TokenIn.Bytes(), path[:20])
+
+	// Bytes 20-23 should be first fee (3000 = 0x000BB8)
+	assert.Equal(t, []byte{0x00, 0x0B, 0xB8}, path[20:23])
+
+	// Bytes 23-43 should be second token
+	assert.Equal(t, opp.Path[0].TokenOut.Bytes(), path[23:43])
+
+	// Bytes 43-46 should be second fee (500 = 0x0001F4)
+	assert.Equal(t, []byte{0x00, 0x01, 0xF4}, path[43:46])
+
+	// Bytes 46-66 should be third token
+	assert.Equal(t, opp.Path[1].TokenOut.Bytes(), path[46:66])
+}
+
+func TestUniswapV3Encoder_buildEncodedPath_SingleStep(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	opp := &arbitrage.Opportunity{
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				Fee:      3000,
+			},
+		},
+	}
+
+	path := encoder.buildEncodedPath(opp)
+
+	// Path should be: token (20) + fee (3) + token (20) = 43 bytes
+	assert.Len(t, path, 43)
+}
+
+func TestUniswapV3Encoder_EncodeExactOutput(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountOut := big.NewInt(1500e6)
+	maxAmountIn := big.NewInt(2e18)
+	fee := uint32(3000)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeExactOutput(
+		tokenIn,
+		tokenOut,
+		amountOut,
+		maxAmountIn,
+		fee,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.swapRouterAddress, to)
+	assert.NotEmpty(t, data)
+	assert.GreaterOrEqual(t, len(data), 4)
+}
+
+func TestUniswapV3Encoder_EncodeMulticall(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	call1 := []byte{0x01, 0x02, 0x03, 0x04}
+	call2 := []byte{0x05, 0x06, 0x07, 0x08}
+	calls := [][]byte{call1, call2}
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeMulticall(calls, deadline)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.swapRouterAddress, to)
+	assert.NotEmpty(t, data)
+	assert.GreaterOrEqual(t, len(data), 4)
+}
+
+func TestUniswapV3Encoder_EncodeMulticall_EmptyCalls(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	calls := [][]byte{}
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeMulticall(calls, deadline)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.swapRouterAddress, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV3Encoder_EncodeMulticall_SingleCall(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	call := []byte{0x01, 0x02, 0x03, 0x04}
+	calls := [][]byte{call}
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeMulticall(calls, deadline)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.swapRouterAddress, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV3Encoder_DifferentFees(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	fees := []uint32{
+		100,   // 0.01%
+		500,   // 0.05%
+		3000,  // 0.3%
+		10000, // 1%
+	}
+
+	for _, fee := range fees {
+		t.Run(string(rune(fee)), func(t *testing.T) {
+			tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+			tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+			amountIn := big.NewInt(1e18)
+			minAmountOut := big.NewInt(1500e6)
+			poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+			recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+			deadline := time.Now().Add(5 * time.Minute)
+
+			to, data, err := encoder.EncodeSwap(
+				tokenIn,
+				tokenOut,
+				amountIn,
+				minAmountOut,
+				poolAddress,
+				fee,
+				recipient,
+				deadline,
+			)
+
+			require.NoError(t, err)
+			assert.NotEmpty(t, to)
+			assert.NotEmpty(t, data)
+		})
+	}
+}
+
+func TestUniswapV3Encoder_ZeroAmounts(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(0)
+	minAmountOut := big.NewInt(0)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	fee := uint32(3000)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		fee,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV3Encoder_LargeAmounts(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+
+	// Max uint256
+	amountIn := new(big.Int)
+	amountIn.SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
+	minAmountOut := new(big.Int)
+	minAmountOut.SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 10)
+
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	fee := uint32(3000)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeSwap(
+		tokenIn,
+		tokenOut,
+		amountIn,
+		minAmountOut,
+		poolAddress,
+		fee,
+		recipient,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.NotEmpty(t, to)
+	assert.NotEmpty(t, data)
+}
+
+func TestUniswapV3Encoder_LongPath(t *testing.T) {
+	encoder := NewUniswapV3Encoder()
+
+	// Create a 5-hop path
+	opp := &arbitrage.Opportunity{
+		InputAmount: big.NewInt(1e18),
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:     common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut:    common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				Fee:         3000,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000001"),
+			},
+			{
+				TokenIn:     common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				TokenOut:    common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+				Fee:         500,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000002"),
+			},
+			{
+				TokenIn:     common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+				TokenOut:    common.HexToAddress("0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9"),
+				Fee:         3000,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000003"),
+			},
+			{
+				TokenIn:     common.HexToAddress("0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9"),
+				TokenOut:    common.HexToAddress("0xDA10009cBd5D07dd0CeCc66161FC93D7c9000da1"),
+				Fee:         500,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000004"),
+			},
+			{
+				TokenIn:     common.HexToAddress("0xDA10009cBd5D07dd0CeCc66161FC93D7c9000da1"),
+				TokenOut:    common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				Fee:         3000,
+				PoolAddress: common.HexToAddress("0x0000000000000000000000000000000000000005"),
+			},
+		},
+	}
+
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000003")
+	minAmountOut := big.NewInt(1e7)
+	deadline := time.Now().Add(5 * time.Minute)
+
+	to, data, err := encoder.EncodeMultiHopSwap(
+		opp,
+		recipient,
+		minAmountOut,
+		deadline,
+	)
+
+	require.NoError(t, err)
+	assert.Equal(t, encoder.swapRouterAddress, to)
+	assert.NotEmpty(t, data)
+
+	// Path should be: 20 + (23 * 5) = 135 bytes
+	path := encoder.buildEncodedPath(opp)
+	assert.Len(t, path, 135)
+}
+
+// Benchmark tests
+func BenchmarkUniswapV3Encoder_EncodeSwap(b *testing.B) {
+	encoder := NewUniswapV3Encoder()
+
+	tokenIn := common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")
+	tokenOut := common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8")
+	amountIn := big.NewInt(1e18)
+	minAmountOut := big.NewInt(1500e6)
+	poolAddress := common.HexToAddress("0x0000000000000000000000000000000000000001")
+	fee := uint32(3000)
+	recipient := common.HexToAddress("0x0000000000000000000000000000000000000002")
+	deadline := time.Now().Add(5 * time.Minute)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _, _ = encoder.EncodeSwap(
+			tokenIn,
+			tokenOut,
+			amountIn,
+			minAmountOut,
+			poolAddress,
+			fee,
+			recipient,
+			deadline,
+		)
+	}
+}
+
+func BenchmarkUniswapV3Encoder_buildEncodedPath(b *testing.B) {
+	encoder := NewUniswapV3Encoder()
+
+	opp := &arbitrage.Opportunity{
+		Path: []arbitrage.SwapStep{
+			{
+				TokenIn:  common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1"),
+				TokenOut: common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				Fee:      3000,
+			},
+			{
+				TokenIn:  common.HexToAddress("0xFF970a61A04b1cA14834A43f5dE4533eBDDB5CC8"),
+				TokenOut: common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f"),
+				Fee:      500,
+			},
+		},
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = encoder.buildEncodedPath(opp)
+	}
+}