look-inside-pytest-tmp-path.md

Look Inside Pytest tmp_path

In Isolate and Debug File Side-Effects with Pytest tmp_path, I wrote about how I use tmp_path in a Pytest fixture to test my py-vmt CLI. During testing of the CLI interface via click's testing utilities, vmt creates, modifies, and reads from files. Isolating that behavior with the tmp_path fixture is useful because it prevents individual test cases from conflicting with one another.

Here is what the fixture looks like at the top of my test file:

# auto fixture for all test cases that monkeypatches the platform dirs to a tmp
# path so that test side-effects don't persist between runs
@pytest.fixture(autouse=True)
def use_tmp_platform_dirs(tmp_path, monkeypatch):
    data_dir = tmp_path / "data"
    config_dir = tmp_path / "config"
    data_dir.mkdir()
    config_dir.mkdir()
    monkeypatch.setattr(CliContext, "get_data_dir", staticmethod(lambda: data_dir))
    monkeypatch.setattr(CliContext, "get_config_dir", staticmethod(lambda: config_dir))

The root of the temp directory is located at tempfile.gettempdir() and the directories from there are organized with this structure:

{temproot}/pytest-of-{user}/pytest-{num}/{testname}/

So, in the case of vmt, I can find the config and data dirs for a specific test run here:

❯ ls /var/folders/zc/q6gnvbgx6kq77828jn38716r0000gn/T/pytest-of-lastword/pytest-2/test_start_status_stop_flow0
config data