How to return a specific value every nth time of a consecutive call with Gmock

Question

In the code Google Mock test snippet there is an EXPECT_CALL that returns True and an argument reference for 200 times.

How can I let the test only return True every nth time. For example return True each 10th call and otherwise return False.

class MockHandler : public Handler
{
    public:
        MOCK_METHOD1(RxMsg, bool(Msg &msg));
}

TEST(TestDispatcher, HandlePing)
{
    auto mockedHandler = make_unique<MockHandler>();
    Msg rxMsg = { REQUEST::REQ_PING, sizeof(DefaultMsg_t), rxMsg.rx,(uint8_t*)"0"};

    EXPECT_CALL(*mockedHandler, 
        RxMsg(_)).Times(checkValue).WillRepeatedly(
            DoAll(SetArgReferee<0>(rxMsg), Return(TRUE)));

    Dispatcher dispatcher(10, mockedHandler);

    for (int i = 0; i < 199; i++)
    {
        dispatcher.RunToCompletion();
    }
}

Answer 1

There are few approaches that might work for you. I like the solution with Invoke as a default action, because it is the most flexible. You didn't provide mcve in your question, so I wrote very simple implementations for the classes you use. Also you made a mistake using unique_ptr for the mock. In 99% of cases is must be shared_ptr, because you are sharing it between testing environment and your System Under Test.

class Msg {};

class Handler {
public:
    virtual bool RxMsg(Msg &msg) = 0;
};

class MockHandler: public Handler
{
public:
    MOCK_METHOD1(RxMsg, bool(Msg &msg));
};

class Dispatcher {
public:
    Dispatcher(std::shared_ptr<Handler> handler): h_(handler) {}
    void run() {
        Msg m;
        std::cout << h_->RxMsg(m) << std::endl;
    }
private:
    std::shared_ptr<Handler> h_;
};

class MyFixture: public ::testing::Test {
protected:
    MyFixture(): mockCallCounter_(0) {
        mockHandler_.reset(new MockHandler);
        sut_.reset(new Dispatcher(mockHandler_));
    }
    void configureMock(int period) {
        ON_CALL(*mockHandler_, RxMsg(_)).WillByDefault(Invoke(
            [this, period](Msg &msg) {
                // you can also set the output arg here
                // msg = something;
                if ((mockCallCounter_++ % period) == 0) {
                    return true;
                }
                return false;
            }));
    }
    int mockCallCounter_;
    std::shared_ptr<MockHandler> mockHandler_;
    std::unique_ptr<Dispatcher> sut_;
};

TEST_F(MyFixture, HandlePing) {
    configureMock(10);
    for (int i = 0; i < 199; i++) {
        sut_->run();
    }
}

At the beginning of each test you should call configureMock method that will Invoke ON_CALL macro setting the default action for your mock. Function passed to Invoke can be any function matching the signature of the method you are overwriting. In this case it;s a function that counts how many times mock has already been called and returns appropriate value. You can also assign some particular object to the msg output argument.