Coroutines are a powerful feature in modern C++ that simplify the asynchronous programming model by making it look like synchronous code. However, testing and mocking coroutines can be a bit tricky. In this blog post, we will explore how to test and mock coroutines in C++.

Testing Coroutines

To test coroutines in C++, you need to ensure that the coroutine behaves as expected when running in an asynchronous context. One way to achieve this is by using testing frameworks that provide support for asynchronous testing, such as Google Test with the EXPECT_XX_ASYNC macros.

Here’s an example of how you can test a coroutine using Google Test:

#include <gtest/gtest.h>
#include <experimental/coroutine>

// Coroutine function
std::experimental::coroutine_handle<> coroFunc() {
    // Coroutine logic goes here
}

TEST(CoroutineTest, TestCoroutine) {
    // Start the coroutine
    auto coro = coroFunc();

    // Check if it is not done yet
    EXPECT_FALSE(coro.done());

    // Resume the coroutine
    coro.resume();

    // Check if it is done
    EXPECT_TRUE(coro.done());

    // Cleanup
    coro.destroy();
}

In this example, we create a test case called TestCoroutine that starts the coroutine, resumes it, and then checks if it is done. We use the coro.destroy() method to clean up the coroutine after the test finishes.

Mocking Coroutines

Mocking coroutines can be a bit more complicated because coroutines are implemented using state machines. However, with the help of mocking frameworks, you can easily mock the behavior of the underlying state machine.

One popular mocking library in C++ is Google Mock, which can be combined with coroutines to mock their behavior.

Here’s an example of how you can mock a coroutine using Google Mock:

#include <gmock/gmock.h>
#include <experimental/coroutine>

// Coroutine function
std::experimental::coroutine_handle<> coroFunc() {
    // Coroutine logic goes here
}

// Mock coroutine with Google Mock
class MockCoroutine {
public:
    MOCK_METHOD0(resume, void());
    MOCK_CONST_METHOD0(done, bool());

    void operator()() {
        resume();
        if (!done()) {
            (*this)();
        }
    }
};

TEST(MockCoroutineTest, TestMockCoroutine) {
    MockCoroutine mock;

    // Set expectations
    EXPECT_CALL(mock, resume());
    EXPECT_CALL(mock, done()).WillOnce(Return(true));

    // Call the mock coroutine
    mock();

    // Verify expectations
    ::testing::Mock::VerifyAndClearExpectations(&mock);
}

In this example, we create a mock class called MockCoroutine that mocks the resume and done methods of the coroutine. We then use the Google Mock macros to set expectations on the mock and verify them at the end of the test case.

By combining Google Test and Google Mock, you can easily test and mock coroutines in C++. This allows you to write robust and reliable asynchronous code that is easily testable.

#C++ #Coroutines #Testing #Mocking