[NIT-2620] Add test for gas estimation with RPC gas limit

execution/nodeInterface/virtual-contracts.go

@@ -141,7 +141,8 @@ func init() {
 			return
 		}
 		posterCost, _ := state.L1PricingState().PosterDataCost(msg, l1pricing.BatchPosterAddress, brotliCompressionLevel)
-		posterCostInL2Gas := arbos.GetPosterGas(state, header.BaseFee, msg.TxRunMode, posterCost)
+		// Use estimate mode because this is used to raise the gas cap, so we don't want to underestimate.
+		posterCostInL2Gas := arbos.GetPosterGas(state, header.BaseFee, core.MessageGasEstimationMode, posterCost)
 		*gascap = arbmath.SaturatingUAdd(*gascap, posterCostInL2Gas)
 	}
 

system_tests/estimation_test.go

@@ -324,3 +324,35 @@ func TestDisableL1Charging(t *testing.T) {
 	_, err = builder.L2.Client.CallContract(ctx, ethereum.CallMsg{To: &addr, Gas: gasWithoutL1Charging, SkipL1Charging: true}, nil)
 	Require(t, err)
 }
+
+func TestGasEstimationWithRPCGasLimit(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	builder := NewNodeBuilder(ctx).DefaultConfig(t, true)
+	cleanup := builder.Build(t)
+	defer cleanup()
+
+	execConfigA := builder.execConfig
+	execConfigA.RPC.RPCGasCap = params.TxGas
+	testClientA, cleanupA := builder.Build2ndNode(t, &SecondNodeParams{execConfig: execConfigA})
+	defer cleanupA()
+	addr := common.HexToAddress("0x12345678")
+	estimateGas, err := testClientA.Client.EstimateGas(ctx, ethereum.CallMsg{To: &addr})
+	Require(t, err)
+	if estimateGas <= params.TxGas {
+		Fatal(t, "Incorrect gas estimate")
+	}
+
+	_, err = testClientA.Client.CallContract(ctx, ethereum.CallMsg{To: &addr}, nil)
+	Require(t, err)
+
+	execConfigB := builder.execConfig
+	execConfigB.RPC.RPCGasCap = params.TxGas - 1
+	testClientB, cleanupB := builder.Build2ndNode(t, &SecondNodeParams{execConfig: execConfigB})
+	defer cleanupB()
+	_, err = testClientB.Client.EstimateGas(ctx, ethereum.CallMsg{To: &addr})
+	if err == nil {
+		Fatal(t, "EstimateGas passed with insufficient gas")
+	}
+}