Function DoGenAndWrite

util/stream/buffered_ut.cpp:77–94

    template <class TOut>
    inline void DoGenAndWrite(TOut&& output, TString& str) {
        TMersenne<ui64> r;
        for (size_t i = 0; i < 43210; ++i) {
            str.append('A' + (r.GenRand() % 10));
        }
        size_t written = 0;
        void* ptr = nullptr;
        while (written < str.size()) {
            size_t bufferSize = output.Next(&ptr);
            UNIT_ASSERT(ptr && bufferSize > 0);
            size_t toWrite = Min(bufferSize, str.size() - written);
            memcpy(ptr, str.begin() + written, toWrite);
            written += toWrite;
            if (toWrite < bufferSize) {
                output.Undo(bufferSize - toWrite);
            }
        }
    }

    Y_UNIT_TEST(TestWriteViaNextAndUndo) {
        TString str1, str2;