'If two different tests have the same error, L{Reporter._groupResults}
includes them together in one of the tuples in the list it returns.'

def test_groupResults(self):

    try:
        raise RuntimeError('foo')
    except RuntimeError:
        self.result.addError(self, sys.exc_info())
        self.result.addError(self.test, sys.exc_info())
    try:
        raise RuntimeError('bar')
    except RuntimeError:
        extra = sample.FooTest('test_bar')
        self.result.addError(extra, sys.exc_info())
    self.result.done()
    grouped = self.result._groupResults(self.result.errors, self.result._formatFailureTraceback)
    self.assertEqual(grouped[0][1], [self, self.test])
    self.assertEqual(grouped[1][1], [extra])
