These tests test for C++ features your compiler might already support. std::string_view, std::apply, and std::invoke are C++17 features. The compiler might already support std::string_view in earlier versions, possibly under the name std::experimental::string_view. ROOT has its own implementation of string_view, if the compiler (or the STL implementation that comes with the compiler) does not have it. Therefore “Failed” = the STL you are using does not provide the corresponding feature. No problem though.