Googletest with CMake

Background

Welcome to 2021. This is my first article for this year and I want to start with a useful tip for C++ unit testing. Unlike other languages, unit testing in C++ has never been as straightforward. However, googletest (also known as “gtest”) has been one of the more well-received testing framework in various organizations, so that’s what I will focus on.

What makes this article slightly different is that unlike the traditional way of defining an entry point for your testing program (ie. a main() function), I will walk through how NOT to do that - how to use googletest with CMake without defining any entry point.

Test case

Let’s suppose that I want to test some function. The standard way to define a test case using gtest is the following:

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// Component under test
#include <myproject/maths.h>

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

using namespace ::testing;

TEST(my_function_test, basic) {
    // Assume that I want to test if myproject::abs()
    // returns the correct absolute value of an integer
    ASSERT_EQ(myproject::abs(-100), 100);
}

As you see, I have defined a test case called my_function_test.basic and it tests if abs returns the correct absolute value - nothing exciting.

However, this is just a function - to run our test case, naturally we want to have some entry point just like any program. There’s one way to do it: define a main function somewhere like this:

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int main(int argc, char **argv) {
    ::testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

While this works, there’s a neat way to get rid of this main function completely while still being able to run our tests.

gtest_main

A main function seems out of place being placed in a directory specifically for test cases. Fortunately, Google agrees with this idea and they’ve provided the gtest_main library that gives a basic implementation of main(). It means that we don’t need an explicit entry point in our program.

CMake

It’s simple to use gtest_main with CMake:

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file(GLOB_RECURSE SRCS CONFIGURE_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp)

set(target, my_project.t)

add_executable(${target} ${SRCS})

find_package(GTest REQUIRED)
include(GoogleTest)

target_link_libraries(${target} PRIVATE
    my_project
    gmock
    GTest::GTest
    GTest::Main
)

gtest_discover_tests(${target})

Or it coule be simpler:

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file(GLOB_RECURSE SRCS CONFIGURE_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp)

set(target, my_project.t)

add_executable(${target} ${SRCS})

target_link_libraries(${target} PRIVATE
    my_project
    gmock
    gtest
    gtest_main
)

gtest_discover_tests(${target})

After building our project, simply run ctest in the build directory and all test cases will run :smiley:.