Setting command line arguments for main function tests

Question

I have a main() function in python that gets command line arguments. Is there a way for me to write pytest tests for this function and define the arguments in the code?

Answer 1

parse_args takes a argv parameter. The docs uses this repeatedly in it's examples

parser = argparse.ArgumentParser()
parser.add_argument('--foo', action='store_true')
parser.add_argument('bar')
parser.parse_known_args(['--foo', '--badger', 'BAR', 'spam'])

where the string list replicates sys.argv[1:] that it would get from the commandline. If the argument is None (or omitted) the parser uses sys.argv[1:].

So if

def main(argv=None):
    # argparse code
    args, other = arg_parser.parse_known_args(argv)
    return args.first_arg

You could test with

main(['foo', '-f','v'])

The unittesting file for argparse.py uses both this approach, and your's of modifying sys.argv directly.

https://docs.python.org/3/library/argparse.html#beyond-sys-argv

https://docs.python.org/3/library/argparse.html#partial-parsing