'Assert that if there are more bytes available to be read from the
receive buffer than would fit into the buffer passed to
:py:obj:`Connection.recv_into`, only as many as fit are written into
it.'

def _doesnt_overfill_test(self, factory):

    output_buffer = factory(5)
    (server, client) = self._loopback()
    server.send(b('abcdefghij'))
    self.assertEqual(client.recv_into(output_buffer), 5)
    self.assertEqual(output_buffer, bytearray(b('abcde')))
    rest = client.recv(5)
    self.assertEqual(b('fghij'), rest)
