op-bindings: add test coverage of the L1 fee constants

`TestL1BlockSlots` will ensure that the values in the
committed storage layout matches the values that are
hard coded in `op-geth`. This is important to handle
because the storage layout may accidentally change in the
future. This will make it very obvious is there are
issues with the storage layout changing.

op-bindings/predeploys/addresses_test.go

@@ -1,8 +1,11 @@
 package predeploys
 
 import (
+	"math/big"
 	"testing"
 
+	"github.com/ethereum-optimism/optimism/op-bindings/bindings"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/stretchr/testify/require"
 )
@@ -12,3 +15,26 @@ func TestGethAddresses(t *testing.T) {
 	// we import geth in the monorepo, and do not want to import op-bindings into geth.
 	require.Equal(t, L1BlockAddr, types.L1BlockAddr)
 }
+
+// TestL1BlockSlots ensures that the storage layout of the L1Block
+// contract matches the hardcoded values in `op-geth`.
+func TestL1BlockSlots(t *testing.T) {
+	layout, err := bindings.GetStorageLayout("L1Block")
+	require.NoError(t, err)
+
+	var l1BaseFeeSlot, overHeadSlot, scalarSlot common.Hash
+	for _, entry := range layout.Storage {
+		switch entry.Label {
+		case "l1FeeOverhead":
+			overHeadSlot = common.BigToHash(big.NewInt(int64(entry.Slot)))
+		case "l1FeeScalar":
+			scalarSlot = common.BigToHash(big.NewInt(int64(entry.Slot)))
+		case "basefee":
+			l1BaseFeeSlot = common.BigToHash(big.NewInt(int64(entry.Slot)))
+		}
+	}
+
+	require.Equal(t, types.OverheadSlot, overHeadSlot)
+	require.Equal(t, types.ScalarSlot, scalarSlot)
+	require.Equal(t, types.L1BaseFeeSlot, l1BaseFeeSlot)
+}