Contemporary C++ projects often use GoogleTest for unit tests. If you’re using GoogleTest, you might be running your tests by launching your test executable directly. What if you want to run your tests in parallel? Unfortunately, GoogleTest doesn’t offer to do that for you, and there’s some confusion and out-of-date advice that comes up when you search for the topic.
Fortunately, if you’re already using CMake, one easy way to run tests in parallel is to use CMake’s ctest tool.
A method
- In your top-level CMakeLists.txt, ensure you have
enable_testing()orinclude(CTest). - Configure and build.
- Run your tests using a command like
ctest [-j|--parallel] n, wherenis your degree of parallelism. By default, ctest doesn’t show output from tests, so I recommend also using--output-on-failure. To show output from all tests, not just failed ones, use[-V|--verbose]. See the ctest documentation for more options.
Discussion
This works by having ctest invoke your test executable many times, once for each test. It uses the GoogleTest feature gtest_filter, which lets you run only specific tests.
As far as I know, there are no limitations with this approach aside from the obvious ones. Most well-written unit tests are already free of dependencies on other tests or on the state of the SUT before the test begins. Most well-written SUTs do not have global state that could introduce correctness or repeatability issues across tests. Therefore, transitioning to parallel test execution is often as simple as “just doing it” by following the above steps.
This is not the only way to parallelize tests with GoogleTest nor to run parallel C++ unit tests in general. For instance, there’s also gtest-parallel, but I’ve never tried it.