Python Unit Test: Mimic a command line argument for test purposes

I am writing a unit test for the following function which is in my_script.py:

def _parse_args():
    parser = argparse.ArgumentParser(
        description='Script to configure appliance.'
    )
    parser.add_argument('--config_file',
                        help='Path to a JSON configuration file') 
    print parser.parse_args()
    return parser.parse_args()

I want to create a unit test to mimic the command line prompt:

myscript.py --config_file test.json

This is what I have so far:

def test_parse_arg_test_config(self):

        test ={
                "name": "test_name",
                "category": "test_category"
            }

        # set the fake command line prompt to be:
        # myscript.py --config_file test
        # (where test is defined above)

        self.assertEquals(my_script._parse_args().config_file, test)

It is obviously incomplete, but I was wondering if I am approaching this the correct way since _parse_args doesn't take in any inputs I don't know a different way to mimic a config file being passed into the function.