Mocking destructor using Die() pattern causes "uninteresting mock" warnings, despite NiceMock

[Michael Dudley]

I'm using googlemock 1.6.0 to set expectations on my class's destructor using the Die() pattern described in the cookbook. I've been using NiceMock to hide "uninteresting mock" warnings, but Die() brings them back.

The tests below demonstrate how

#include "gmock/gmock.h"
#include "gtest/gtest.h"

using ::testing::NiceMock;

struct MyObject {
    virtual ~MyObject() {}
    virtual void MyFunction() = 0;
};

struct MyObjectMock : public MyObject {
    virtual ~MyObjectMock() {}
    MOCK_METHOD0(MyFunction, void ());
};

struct MyDieObjectMock : public MyObject {
    virtual ~MyDieObjectMock() { Die(); }
    MOCK_METHOD0(Die, void ());
    MOCK_METHOD0(MyFunction, void ());
};

struct MyObjectTest : public ::testing::Test {};

TEST_F(MyObjectTest, NickMockPreventsUninterestingWarning) {
    // Uninteresting function warnings are suppressed here, as expected
    NiceMock<MyObjectMock> lMyObject;
    lMyObject.MyFunction();
}

TEST_F(MyObjectTest, CallToDieTriggersUninterestingWarning) {
    // Uninteresting function warning about Die gets raised here, but shouldn't
    NiceMock<MyDieObjectMock> lMyObject;
    lMyObject.MyFunction();
}

And just for completeness, the output I get is:

[----------] 2 tests from MyObjectTest
[ RUN      ] MyObjectTest.NickMockPreventsUninterestingWarning
[       OK ] MyObjectTest.NickMockPreventsUninterestingWarning (0 ms)
[ RUN      ] MyObjectTest.CallToDieTriggersUninterestingWarning

GMOCK WARNING:
Uninteresting mock function call - returning directly.
    Function call: Die()
Stack trace:
[       OK ] MyObjectTest.CallToDieTriggersUninterestingWarning (4 ms)
[----------] 2 tests from MyObjectTest (5 ms total)

I had expected the "uninteresting mock function" warning about Die() to be suppressed.

Thanks!

[Vlad Losev]

I believe this is an artifact of how NiceMock is implemented. NiceMock<T> is a subclass of T, and when the T's destructor receives control, NiceMock's destructor has already exited, and the instance is no longer considered to be NiceMock, but T. When the Die invocation calls the virtual function that's to provide a reaction to the call, that will be T's version, not NiceMock's. Essentially, NiceMock loses its politeness in the destructor.

This is not easy to fix, and I suggest as a workaround you invoke EXPECT_CALL(lMyObject, die()).Times(AnyNumber()) in your test. Once you are ready to act on that call, add some conditions or actions to that expectation.

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[Zhanyong Wan (λx.x x)]

Excellent analysis, Vlad!

Another option is to use a separate check point object instead of adding a Die() method on the mock itself:

https://code.google.com/p/googlemock/wiki/CookBook#Using_Check_Points

Long term, we should make mocks nice by default and this will become a moot issue.

--
Zhanyong

[Billy Donahue]

That would just be shifting the problem to the StrictMock and NaggyMock wrappers.

[Zhanyong Wan (λx.x x)]

I meant that Michael's particular problem (which uses NiceMock) will become moot.

--
Zhanyong