FIXTURES_REQUIRED does not issue a warning or error if any of the required fixtures are non-existent
nonexistent_fixture is not a test fixture that has been defined, the following CMake command has no effect.
set_tests_properties( test_with_unmet_required_fixtures PROPERTIES FIXTURES_REQUIRED nonexistent_fixture )
In my opinion, this is not good. It would be preferred that CMake emit an error at configure-time, or a warning at configure-time and skip the test at test-time.