tests: handle 0x-prefixed rlp hex in tests

tests/rlp_test_util.go

@@ -42,9 +42,22 @@ type RLPTest struct {
 	Out string
 }
 
+// FromHex returns the bytes represented by the hexadecimal string s.
+// s may be prefixed with "0x".
+// This is copy-pasted from bytes.go, which does not return the error
+func FromHex(s string) ([]byte, error) {
+	if len(s) > 1 && (s[0:2] == "0x" || s[0:2] == "0X") {
+		s = s[2:]
+	}
+	if len(s)%2 == 1 {
+		s = "0" + s
+	}
+	return hex.DecodeString(s)
+}
+
 // Run executes the test.
 func (t *RLPTest) Run() error {
-	outb, err := hex.DecodeString(t.Out)
+	outb, err := FromHex(t.Out)
 	if err != nil {
 		return fmt.Errorf("invalid hex in Out")
 	}