def server():
            data = yield tb.read(4)
            self.assertEqual(data, b'AAAA')
            yield tb.write(b'OK')

            data = yield tb.read(4)
            self.assertEqual(data, b'BBBB')
            yield tb.write(b'SPAM')

            def prog():
                try:
                    yield tb.starttls(client_sslctx)
                    yield tb.connect(addr)
                    yield tb.write(A_DATA)

                    data = yield tb.read(2)
                    self.assertEqual(data, b'OK')

                    yield tb.write(B_DATA)
                    data = yield tb.read(4)
                    self.assertEqual(data, b'SPAM')

                    yield tb.close()

                except Exception as ex:
                    self.loop.call_soon_threadsafe(fut.set_exception, ex)
                else:
                    self.loop.call_soon_threadsafe(fut.set_result, None)

 def srv_gen():
     yield tb.write(b'helo')
     data = yield tb.read(4 * _SIZE)
     self.assertEqual(data, b'ehlo' * _SIZE)
     yield tb.write(b'O')
     yield tb.write(b'K')