Call a program with threading daemon in python

I have an encryption project in python and i want to write an end to end test for whole project.

I can run the project in the command line, like this:

python -m serve -c config.json

for an end to end test, I wrote this test function, but when I ran it, an error occurs while everything in a simple run of the project from the command line is fine.

    def test_assert_end_to_end(self):
        args = []

        config = load_config(args, "config.json")

        t = threading.Thread(target=serve.run, name='serve', args=(args, ))
        t = threading.Thread(target=serve.run, name='serve', args=(config,))
        t.daemon = True
        t.start()

        self.unseal()

        plain_data = bytes(''.join([chr(random.randint(0, 128))
                                   for i in range(EndToEndTest.SIZE_OF_DATA_TO_ENCRYPT * 1024 * 1024)]), "utf-8")

        EncryptResponseBytes = self.encrypt(plain_data)
        DecryptResponseBytes = self.decrypt(EncryptResponseBytes)

        self.assertEqual(plain_data, DecryptResponseBytes)

this is error's log:

    signal.signal(signal.SIGTERM, self._graceful_exit)
  File "/usr/lib/python3.6/signal.py", line 47, in signal
    handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
ValueError: signal only works in main threa

Anyone has any idea, how can I fix this error?