def METHOD_NAME(self) -> None:
    """
    Set C{fileLogObserverFactory} to the default appropriate for the
    chosen C{logFile}.
    """
    if "fileLogObserverFactory" not in self:
        logFile = self["logFile"]
        if hasattr(logFile, "isatty") and logFile.isatty():
            self["fileLogObserverFactory"] = textFileLogObserver
            self["logFormat"] = "text"
        else:
            self["fileLogObserverFactory"] = jsonFileLogObserver
            self["logFormat"] = "json"