How to mock a Function arguments with no operator== using Gmock

Question

I am using Gmock for unit tests. I have function who receive protobuf message as an argument. The problem is that when I'm testing the function with expected value it gives me an error of missing operator==. I found similar problem here google-protocol-buffers-compare

class ClientReaderWriterMock : public ClientReaderWriterIf {
 public:
  virtual ~ClientReaderWriterMock() = default;
  MOCK_METHOD1(Write, bool(const Msg&));
  MOCK_METHOD1(Read, bool(Msg*));
};

TEST_F(controller_Test, receive_message) {
Msg msg;
.
.
.
EXPECT_CALL(*clientReaderWriterMockObj, Write(msg));
.
.
.
}

I receive the following error:

###>/third_party/googletest/googletest/include/gtest/gtest-matchers.h: In instantiation of ‘bool testing::internal::AnyEq::operator()(const A&, const B&) const [with A = Msg; B = Msg]’: /###>/third_party/googletest/googletest/include/gtest/gtest-matchers.h:549:18: required from ‘bool testing::internal::ComparisonBase<D, Rhs, Op>::Impl<Lhs, >::MatchAndExplain(Lhs, testing::MatchResultListener*) const [with Lhs = const Msg&; = Msg; D = testing::internal::EqMatcher; Rhs = Msg; Op = testing::internal::AnyEq]’ /###>/third_party/googletest/googletest/include/gtest/gtest-matchers.h:547:10: required from here /###>/third_party/googletest/googletest/include/gtest/gtest-matchers.h:211:60: error: no match for ‘operator==’ (operand types are ‘const Msg’ and ‘const Msg’) 211 | bool operator()(const A& a, const B& b) const { return a == b; } In file included from /###>/tests/unit/test.cpp:2: /###>/third_party/googletest/googletest/include/gtest/gtest.h:1535:13: note: candidate: ‘bool testing::internal::operator==(testing::internal::faketype, testing::internal::faketype)’ 1535 | inline bool operator==(faketype, faketype) { return true; } /###>/third_party/googletest/googletest/include/gtest/gtest.h:1535:24: note: no known conversion for argument 1 from ‘const Msg’ to ‘testing::internal::faketype’ 1535 | inline bool operator==(faketype, faketype) { return true; }

Quarra Quarra · Accepted Answer · 2020-12-17T10:23:42

When an expect call is set on a function with some arguments, the Eq matcher is used (implicitly), so the line:

EXPECT_CALL(*clientReaderWriterMockObj, Write(msg));

is actually:

EXPECT_CALL(*clientReaderWriterMockObj, Write(Eg(msg)));

Eq matcher will try to invoke operator== (which is missing as you noticed). In such case, you can define your own matcher:

MATCHER_P(CustomMatcher, expected, "Msg doesn't match!") {
    // your comparision code here
    return arg.Field() == expected.Field();
}
[...]
EXPECT_CALL(*clientReaderWriterMockObj, Write(CustomMatcher(msg)));

How to mock a Function arguments with no operator== using Gmock

1 Answers