Class BufferedWriter

Lib/test/test_io/test_textio.py:1028–1034

        # on the underlying binary buffered object.
        flush_called, write_called = [], []
        class BufferedWriter(self.BufferedWriter):
            def flush(self, *args, **kwargs):
                flush_called.append(True)
                return super().flush(*args, **kwargs)
            def write(self, *args, **kwargs):
                write_called.append(True)
                return super().write(*args, **kwargs)

        rawio = self.BytesIO()
        data = b"a"