def METHOD_NAME(fake_filesystem, srv, caplog, item):
    """
    Dispatch a single message and prove it is stored in the designated file.
    """
    module = mqttwarn.services.file
    outcome = module.plugin(srv, item)
    assert os.path.exists("/tmp/testdrive.log")
    assert outcome is True
    assert "Writing to file `/tmp/testdrive.log'" in caplog.messages
    assert open("/tmp/testdrive.log", mode="r", encoding="utf-8").read() == "\u26bd Notification message \u26bd"