def addError(self, test, error):
        """
        If the error is a L{util.DirtyReactorAggregateError}, instead of
        reporting it as a normal error, throw a warning.
        """

        if (isinstance(error, Failure)
            and error.check(util.DirtyReactorAggregateError)):
            warnings.warn(error.getErrorMessage())
        else:
            self._originalReporter.addError(test, error)

        If the error is a L{util.DirtyReactorAggregateError}, instead of
        reporting it as a normal error, throw a warning.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/reporter.py