Unit Testing And Mocking

gtest (Google Test)

gtest (a.k.a Google Test) is an open-source C++ unit testing framework developed and maintained by Google.

The introduction of lambda functions in C++11 make certain C++ unit tests much less verbose. This includes tests where you want to verify that a boost::signal was emitted:

bool lambdaCalled = false;

// Use lambda notation to provide a "slot"
// for the signal
mySignal.connect([&]() {
    lambdaCalled = true;
});

// Do whatever is needed to fire the signal. In this simplistic
//case, we will fire the signal directly.
mySignal();

EXPECT_EQ(true, lambdaCalled);

Adding Timeouts To Google Unit Tests

You can timeouts to Google unit tests by defining the following macros:

#include <future>

#define TEST_TIMEOUT_BEGIN \
    std::promise<bool> promisedFinished; \
    auto futureResult = promisedFinished.get_future(); \
    std::thread([&](std::promise<bool>& finished) {

#define TEST_TIMEOUT_FAIL_END(X) \
    finished.set_value(true); \
    }, std::ref(promisedFinished)).detach(); \
    EXPECT_TRUE(futureResult.wait_for(std::chrono::milliseconds(X)) != std::future_status::timeout);

#define TEST_TIMEOUT_SUCCESS_END(X) \
    finished.set_value(true); \
    }, std::ref(promisedFinished)).detach(); \
    EXPECT_FALSE(futureResult.wait_for(std::chrono::milliseconds(X)) != std::future_status::timeout);

You then use these macros in the following fashion:

TEST(UnitTestModule, TimeoutTest)
{
    TEST_TIMEOUT_BEGIN
    EXPECT_EQ(10, function_takes_a_long_time());
    TEST_TIMEOUT_FAIL_END(1000)
}

Any code within the TEST_TIMEOUT_BEGIN and TEST_TIMEOUT_FAIL_END(1000) macros that takes longer that 1000ms will be aborted, and the test will fail. Credit for the above macros goes to https://antonlipov.blogspot.ca/2015/08/how-to-timeout-tests-in-gtest.html.

gmock (Google Mock)

gmock (a.k.a Google Mock) is an open-source C++ mocking library developed and maintained by Google. It is NOT a unit testing framework, but can be used in conjunction with gtest to provide a fully feature unit testing system.

One disadvantage of gmock is that all class methods that you want to mock must be declared virtual. This increases the computational overhead of the class, and it may not be possible to add virtual if a 3rd party wrote/maintains the class of interest.

UnitTest++

UnitTest++ is a small, lightweight, but capable unit test library for C++ code.

Example output from UnitTest++ when one of the tests fails.

Example output from UnitTest++ when one of the tests fails.

Running Just One Test Suite

The unit tests can be grouped into “Suites” which are designed to be for grouping together similar tests. You can also run just one test suite, useful for preventing yourself getting swamped with errors when debugging failed unit tests. The documentation on many sites on how to run just one suite is wrong as of June 2013 (maybe they recently updated the code). Here is a way I found of doing it:

int main()
{
    UnitTest::TestReporterStdout reporter;
    UnitTest::TestRunner runner(reporter);

    return runner.RunTestsIf(
        UnitTest::Test::GetTestList(),
        "Test Suite Name",
        UnitTest::True(),
        0);
}

Replace “Test Suite Name” with the name of the test suite you want to run.

catch2

catch2 is a popular C++ unit test library that uses CMake as its build system.

v2 of catch was a header-only library, presumably choosen because of the ease-of-installation (copy the header file into your project, include it and you’re done). From v3 they switched to a more traditional header/source style library. The main reason for this was compile-time performance. With the header-only library you had to re-compile catch2 everytime you wanted to recompile your unit tests. This could take 30-60s on fast machines. With the more traditional header/source style library, you only need to compile catch2 once, and then you can link against the statis library everytime you rebuild your unit tests, shortening the compile time to a second or less.

You can easily grab a version of catch2 by using CMake’s FetchContent functionality. It is the simplist way, CMake will automatically download the library for you.

CMakeLists.txt

Include(FetchContent)

FetchContent_Declare(
  Catch2
  GIT_REPOSITORY https://github.com/catchorg/Catch2.git
  GIT_TAG        v3.4.0 # or a later release
)

FetchContent_MakeAvailable(Catch2)

add_executable(tests test.cpp)
target_link_libraries(tests PRIVATE Catch2::Catch2WithMain)