gh-131178: Add tests for sysconfig command-line interface

[LamentXU123]

As doc points out, we can use sysconfig lib directly as a script to obtain configs.

This PR add tests for this feature.

PS: I notice that the CLI actually has a --generare-posix-vars attribute that is undocumented. I don't think we need to add test for that (maybe this is an internal function or what. If not I think we can add document for this later)

def _main():
    """Display all information sysconfig detains."""
    if '--generate-posix-vars' in sys.argv:
        _generate_posix_vars()
        return
    print(f'Platform: "{get_platform()}"')
    print(f'Python version: "{get_python_version()}"')
    print(f'Current installation scheme: "{get_default_scheme()}"')
    print()
    _print_dict('Paths', get_paths())
    print()
    _print_dict('Variables', get_config_vars())

• Issue: Add tests for command-line interface #131178

[cmaloney]

👍 to not documenting --generate-posix-vars. Other comments inline

[cmaloney]

The docs say that all these values should be present in the text, could we check for them in the test? That way the test validates they're there (and if the output changes, know it needs to change)

get_platform(), get_python_version(), get_path() and get_config_vars().

[LamentXU123]

I will add a stricter test case by mocking an output and directly compare the mock output and the real one.

[cmaloney]

From what I can see in the base issue the pattern for these tests is to use contextlib.redirect_stdout + call the function which implements main directly (sysconfig._main) rather than run / use a subprocess.

See for example: https://github.com/python/cpython/pull/131275/files#diff-eabc91c9e7a2586ffc6ca849d6636e74e28825a4515745c280b045dbdf857e39R723-R727

That should also fix the WASI check which is currently failing with: OSError: [Errno 58] wasi does not support processes.

[LamentXU123]

Ah! Thank you. I am really stuck on how to fix the WASI test.

[LamentXU123]

Actually we've already got this for the CLI test:

    def test_main(self):
        # just making sure _main() runs and returns things in the stdout
        with captured_stdout() as output:
            _main()
        self.assertTrue(len(output.getvalue().split('\n')) > 0)

So we don't need to change things(why are the CLI test mixing with others XD) .Sorry that I overlook this.