def test_encodableUnicodeEnvironment(self):
        """
        Test C{os.environ} (inherited by every subprocess on Windows) that
        contains an ascii-encodable Unicode string. This is different from
        passing Unicode environment explicitly to spawnProcess (which is not
        supported on Python 2).
        """
        os.environ[self.goodKey] = self.goodValue
        self.addCleanup(operator.delitem, os.environ, self.goodKey)

        p = GetEnvironmentDictionary.run(reactor, [], properEnv)
        def gotEnvironment(environ):
            self.assertEqual(
                environ[self.goodKey.encode('ascii')],
                self.goodValue.encode('ascii'))
        return p.getResult().addCallback(gotEnvironment)

        Test C{os.environ} (inherited by every subprocess on Windows) that
        contains an ascii-encodable Unicode string. This is different from
        passing Unicode environment explicitly to spawnProcess (which is not
        supported on Python 2).
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_process.py