op-node: system config derive tests

Adds test coverage for the system config derivation
for each different type of event. It would be nice to
fuzz this in the future.

op-node/rollup/derive/system_config_test.go

+package derive
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/ethereum-optimism/optimism/op-node/eth"
+	"github.com/ethereum/go-ethereum/accounts/abi"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	// ABI encoding helpers
+	dynBytes, _ = abi.NewType("bytes", "", nil)
+	address, _  = abi.NewType("address", "", nil)
+	uint256T, _ = abi.NewType("uint256", "", nil)
+	addressArgs = abi.Arguments{
+		{Type: address},
+	}
+	bytesArgs = abi.Arguments{
+		{Type: dynBytes},
+	}
+	twoUint256 = abi.Arguments{
+		{Type: uint256T},
+		{Type: uint256T},
+	}
+	oneUint256 = abi.Arguments{
+		{Type: uint256T},
+	}
+)
+
+// TestProcessSystemConfigUpdateLogEvent tests the parsing of an event and mutating the
+// SystemConfig. The hook will build the ABI encoded data dynamically. All tests create
+// a new SystemConfig and apply a log against it and then assert that the mutated system
+// config is equal to the defined system config in the test.
+func TestProcessSystemConfigUpdateLogEvent(t *testing.T) {
+	tests := []struct {
+		name   string
+		log    *types.Log
+		config eth.SystemConfig
+		hook   func(*testing.T, *types.Log) *types.Log
+		err    bool
+	}{
+		{
+			// The log data is ignored by consensus and no modifications to the
+			// system config occur.
+			name: "SystemConfigUpdateUnsafeBlockSigner",
+			log: &types.Log{
+				Topics: []common.Hash{
+					ConfigUpdateEventABIHash,
+					ConfigUpdateEventVersion0,
+					SystemConfigUpdateUnsafeBlockSigner,
+				},
+			},
+			hook: func(t *testing.T, log *types.Log) *types.Log {
+				addr := common.Address{}
+				data, err := addressArgs.Pack(&addr)
+				require.NoError(t, err)
+				log.Data = data
+				return log
+			},
+			config: eth.SystemConfig{},
+			err:    false,
+		},
+		{
+			// The batcher address should be updated.
+			name: "SystemConfigUpdateBatcher",
+			log: &types.Log{
+				Topics: []common.Hash{
+					ConfigUpdateEventABIHash,
+					ConfigUpdateEventVersion0,
+					SystemConfigUpdateBatcher,
+				},
+			},
+			hook: func(t *testing.T, log *types.Log) *types.Log {
+				addr := common.Address{19: 0xaa}
+				addrData, err := addressArgs.Pack(&addr)
+				require.NoError(t, err)
+				data, err := bytesArgs.Pack(addrData)
+				require.NoError(t, err)
+				log.Data = data
+				return log
+			},
+			config: eth.SystemConfig{
+				BatcherAddr: common.Address{19: 0xaa},
+			},
+			err: false,
+		},
+		{
+			// The overhead and the scalar should be updated.
+			name: "SystemConfigUpdateGasConfig",
+			log: &types.Log{
+				Topics: []common.Hash{
+					ConfigUpdateEventABIHash,
+					ConfigUpdateEventVersion0,
+					SystemConfigUpdateGasConfig,
+				},
+			},
+			hook: func(t *testing.T, log *types.Log) *types.Log {
+				overhead := big.NewInt(0xff)
+				scalar := big.NewInt(0xaa)
+				numberData, err := twoUint256.Pack(overhead, scalar)
+				require.NoError(t, err)
+				data, err := bytesArgs.Pack(numberData)
+				require.NoError(t, err)
+				log.Data = data
+				return log
+			},
+			config: eth.SystemConfig{
+				Overhead: eth.Bytes32{31: 0xff},
+				Scalar:   eth.Bytes32{31: 0xaa},
+			},
+			err: false,
+		},
+		{
+			// The gas limit should be updated.
+			name: "SystemConfigUpdateGasLimit",
+			log: &types.Log{
+				Topics: []common.Hash{
+					ConfigUpdateEventABIHash,
+					ConfigUpdateEventVersion0,
+					SystemConfigUpdateGasLimit,
+				},
+			},
+			hook: func(t *testing.T, log *types.Log) *types.Log {
+				gasLimit := big.NewInt(0xbb)
+				numberData, err := oneUint256.Pack(gasLimit)
+				require.NoError(t, err)
+				data, err := bytesArgs.Pack(numberData)
+				require.NoError(t, err)
+				log.Data = data
+				return log
+			},
+			config: eth.SystemConfig{
+				GasLimit: 0xbb,
+			},
+			err: false,
+		},
+		{
+			name: "SystemConfigOneTopic",
+			log: &types.Log{
+				Topics: []common.Hash{
+					ConfigUpdateEventABIHash,
+				},
+			},
+			hook: func(t *testing.T, log *types.Log) *types.Log {
+				return log
+			},
+			config: eth.SystemConfig{},
+			err:    true,
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			config := eth.SystemConfig{}
+
+			err := ProcessSystemConfigUpdateLogEvent(&config, test.hook(t, test.log))
+			if test.err {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+			require.Equal(t, config, test.config)
+		})
+	}
+}