[Testing] Passing env through invoke() does not work

Explanation

I’m building a multi-commands cli with persistent configuration stored in ~/.config/myapp Each time cli runs, it parses this file and passes it to context to be available to sub-commands. The init command builds and writes configuration on disk. For testing I want to use isolated_filesystem() and write config on it, using invoke() with env var.

src/config.py

if 'TMP_DIR' in environ:
    CONFIG_DIRECTORY = Path(environ['TMP_DIR'])
else:
    CONFIG_DIRECTORY = Path.home().joinpath(".config/myapp")

CONFIG_FILE = CONFIG_DIRECTORY.joinpath("config.json")

test/init_test.py

def test_init(runner):
    with runner.isolated_filesystem() as fs:
        # Adding config location to env
        env = environ.copy()
        env['TMP_DIR'] = fs
        # Running init cmd with env
        res = runner.invoke(cli, ['--verbose', 'init', '.'], env=env)
        assert res.exit_code == 0
        assert fs in res.output

Expected Behavior

Init command should exit successfully and print to stdout the directory where config file was created like this:

working directory initialized in /tmp/tmplmw_fea6

Actual Behavior

TMP_DIR env is not passed to init command, so config is loaded from ~/.config/myapp even in testing.

Environment

I use virtualenv with:

• Python version: 3.6.9
• Click version: 7.1.1
• Pytest version: 5.4.1

Thank you in advance 😄

[amy-lei]

Seems the issue is that the value of CONFIG_FILE was already set the moment you imported from config, and this happens before the env gets updated. So although the value is indeed there (can check by printing environ.get("TMP_DIR") inside of read_config), the actual value of CONFIG_FILE used inside of the function body will not reflect that.

I made some changes to read_config so that it updates the value of CONFIG_FILE before evaluating the rest of the body, and the output is now DEBUG config file loaded from /tmp/tmpjn_b9xq8/config.json. Does this match the behavior you were expecting? Here is the code forked from your replit: https://repl.it/join/ljsynukg-amylei3

[LucasVanHaaren]

I made some changes to read_config so that it updates the value of CONFIG_FILE before evaluating the rest of the body, and the output is now DEBUG config file loaded from /tmp/tmpjn_b9xq8/config.json. Does this match the behavior you were expecting? […]

Yes, it’s definitely the expecting behavior 👌 Thank you all for your time.