Method overflow

tests/framework/src/doctest.cpp:3692–3695

        std::streamsize xsputn(const char_type*, std::streamsize count) override { return count; }

        int_type overflow(int_type ch) override {
            setp(std::begin(buf), std::end(buf));
            return traits_type::not_eof(ch);
        }
    } discardBuf;

public: