def test_concurrent(self):
                """
                Try to start another runner in the same working directory and
                assert that it raises L{_WorkingDirectoryBusy}.
                """
                self.assertRaises(
                    util._WorkingDirectoryBusy,
                    secondRunner.run, ConcurrentCase('test_failure'))

                Try to start another runner in the same working directory and
                assert that it raises L{_WorkingDirectoryBusy}.
                
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_runner.py