Function toLowerCh

unittests/catch.hpp:9588–9590

        return s.find( infix ) != std::string::npos;
    }
    char toLowerCh(char c) {
        return static_cast<char>( std::tolower( c ) );
    }
    void toLowerInPlace( std::string& s ) {
        std::transform( s.begin(), s.end(), s.begin(), toLowerCh );
    }