'Make sure an existing message doesn\'t stop waiting twice.
wait_for checks existing messages (see above), but we don\'t want it to
automatically proceed if we already *did* use wait_for on one of the
existing messages, as that makes it likely it\'s not what we actually
want.'

def test_existing_message_already_waited(self, pyproc):

    pyproc.code = "time.sleep(0.1);    print('foobar')"
    pyproc.start()
    pyproc.wait_for(data='foobar')
    with pytest.raises(testprocess.WaitForTimeout):
        pyproc.wait_for(data='foobar', timeout=100)
