def test_detectFilesRemoved(self):
        """
        Check that when a dropin file is removed, L{plugin.getPlugins} doesn't
        return it anymore.
        """
        FilePath(__file__).sibling('plugin_extra1.py'
            ).copyTo(self.package.child('pluginextra.py'))
        try:
            # Generate a cache with pluginextra in it.
            list(plugin.getPlugins(ITestPlugin, self.module))

        finally:
            self._unimportPythonModule(
                sys.modules['mypackage.pluginextra'],
                True)
        plgs = list(plugin.getPlugins(ITestPlugin, self.module))
        self.assertEqual(1, len(plgs))

        Check that when a dropin file is removed, L{plugin.getPlugins} doesn't
        return it anymore.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_plugin.py