Added test-deduct-gas test

precompile/contract/utils.go

@@ -15,13 +15,13 @@ const (
 	ReadGasCostPerSlot  = 5_000
 )
 
-var functionSignatureRegex = regexp.MustCompile(`\w+\((\w*|(\w+,)+\w+)\)`)
+var FunctionSignatureRegex = regexp.MustCompile(`\w+\((\w*|(\w+,)+\w+)\)`)
 
 // MustCalculateFunctionSelector returns the 4 byte function selector that results from [functionSignature]
 // Ex. the function setBalance(addr address, balance uint256) should be passed in as the string:
 // "setBalance(address,uint256)"
 func MustCalculateFunctionSelector(functionSignature string) []byte {
-	if !functionSignatureRegex.MatchString(functionSignature) {
+	if !FunctionSignatureRegex.MatchString(functionSignature) {
 		panic(fmt.Errorf("invalid function signature: %q", functionSignature))
 	}
 	hash := crypto.Keccak256([]byte(functionSignature))

precompile/contract/utils_test.go

@@ -1,12 +1,14 @@
 // (c) 2019-2020, Ava Labs, Inc. All rights reserved.
 // See the file LICENSE for licensing terms.
 
-package contract
+package contract_test
 
 import (
 	"testing"
 
-	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/ethereum/go-ethereum/precompile/contract"
 )
 
 func TestFunctionSignatureRegex(t *testing.T) {
@@ -61,6 +63,46 @@ func TestFunctionSignatureRegex(t *testing.T) {
 			pass: false,
 		},
 	} {
-		assert.Equal(t, test.pass, functionSignatureRegex.MatchString(test.str), "unexpected result for %q", test.str)
+		require.Equal(t, test.pass, contract.FunctionSignatureRegex.MatchString(test.str), "unexpected result for %q", test.str)
+	}
+}
+
+func TestDeductGas(t *testing.T) {
+	for _, tc := range []struct {
+		desc         string
+		suppliedGas  uint64
+		requiredGas  uint64
+		remainingGas uint64
+		err          string
+	}{
+		{
+			desc:        "not enough gas",
+			suppliedGas: 0,
+			requiredGas: 100,
+			err:         "out of gas",
+		},
+		{
+			desc:         "enough gas",
+			suppliedGas:  100,
+			requiredGas:  100,
+			remainingGas: 0,
+		},
+		{
+			desc:         "more than enough gas",
+			suppliedGas:  200,
+			requiredGas:  100,
+			remainingGas: 100,
+		},
+	} {
+		t.Run(tc.desc, func(t *testing.T) {
+			remainingGas, err := contract.DeductGas(tc.suppliedGas, tc.requiredGas)
+			if tc.err != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), "out of gas")
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, tc.remainingGas, remainingGas)
+			}
+		})
 	}
 }