def test_process(self):
        """
        Test running a process: check its output, it exitCode, some property of
        signalProcess.
        """
        scriptPath = b"twisted.test.process_tester"
        d = defer.Deferred()
        p = TestProcessProtocol()
        p.deferred = d
        reactor.spawnProcess(p, pyExe, [pyExe, b"-u", b"-m", scriptPath],
                             env=properEnv)
        def check(ignored):
            self.assertEqual(p.stages, [1, 2, 3, 4, 5])
            f = p.reason
            f.trap(error.ProcessTerminated)
            self.assertEqual(f.value.exitCode, 23)
            # would .signal be available on non-posix?
            # self.assertIsNone(f.value.signal)
            self.assertRaises(
                error.ProcessExitedAlready, p.transport.signalProcess, 'INT')
            try:
                import process_tester, glob
                for f in glob.glob(process_tester.test_file_match):
                    os.remove(f)
            except:
                pass
        d.addCallback(check)
        return d

        Test running a process: check its output, it exitCode, some property of
        signalProcess.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_process.py