Function count

unittests/catch.hpp:2525–2533

        namespace Detail {
            template <typename InputIterator, typename T>
            size_t count(InputIterator first, InputIterator last, T const& item) {
                size_t cnt = 0;
                for (; first != last; ++first) {
                    if (*first == item) {
                        ++cnt;
                    }
                }
                return cnt;
            }
            template <typename InputIterator, typename T>
            bool contains(InputIterator first, InputIterator last, T const& item) {
                for (; first != last; ++first) {