def _printResults(self, flavor, errors, formatter):
        """
        Print a group of errors to the stream.

        @param flavor: A string indicating the kind of error (e.g. 'TODO').
        @param errors: A list of errors, often L{failure.Failure}s, but
            sometimes 'todo' errors.
        @param formatter: A callable that knows how to format the errors.
        """
        for reason, cases in self._groupResults(errors, formatter):
            self._writeln(self._doubleSeparator)
            self._writeln(flavor)
            self._write(reason)
            self._writeln('')
            for case in cases:
                self._writeln(case.id())

        Print a group of errors to the stream.

        @param flavor: A string indicating the kind of error (e.g. 'TODO').
        @param errors: A list of errors, often L{failure.Failure}s, but
            sometimes 'todo' errors.
        @param formatter: A callable that knows how to format the errors.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/reporter.py