Can I use google mocks to check method parameters without setting an expectation in advance?

Question

I have a situation where I want to check if a mock object method was called with parameter X, but the test gets access to X only after the mock is invoked, so I can't set an EXPECT_CALL beforehand.

E.g.

// The class I'm testing.
class Maker
{
    void register(Listener& lis);
    Obj& make()
    {
        // make new Obj o
        // call created(o) on registered Listener  
        // return o
    }
}

class Listener
{
    virtual void created(Obj& o) = 0;
}

// The test
Listener lis;
Maker maker;
maker.register(lis);

Obj& o = maker.make();

// Check that lis was invoked using param o...how?

Can i do this with google mocks? What is the most elegant / readable way of doing this using google mocks?

Obviously I can make my own MockListener which will record invocation parameters, instead of using google mocks. But I'm hoping google mocks would preesnt a more readable mechanism, similar to EXPECT_CALL.

Answer 1

You can use the SaveArg<N> action to save the value of the parameter with which Listener::created(Obj&) is called, so you can compare its value to the one returned by maker.make() afterwards.

This will require that you provide equality operator for class Obj, i.e. bool operator==(const Obj&, const Obj&).

Your test could then look like this:

class ListenerMock : public Listener
{
public:
    MOCK_METHOD1(created, void(Obj&));
};

TEST(MakerTest, make_registersObject)
{
    ListenerMock lis;
    Maker maker;
    maker.register(lis);

    Obj createdArg;
    EXPECT_CALL(lis, created(_))
        .Times(1)
        .WillOnce(SaveArg<0>(&createdArg));

    Obj& o = maker.make();

    ASSERT_EQ(createdArg, o);
}