def resetEnvironment(self):
        """
        Change the environment to what it should be just as the test is
        starting.
        """
        self.unsetEnvironment()
        sys.path.extend([x.path for x in [self.devPath,
                                          self.systemPath,
                                          self.appPath]])

        Change the environment to what it should be just as the test is
        starting.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_plugin.py