Function cleanupSingletons

tutorials/external/catch.hpp:11166–11172

        getSingletons()->push_back( singleton );
    }
    void cleanupSingletons() {
        auto& singletons = getSingletons();
        for( auto singleton : *singletons )
            delete singleton;
        delete singletons;
        singletons = nullptr;
    }

} // namespace Catch
// end catch_singletons.cpp