What determines conftest hook order?

[scott-codecov]

I noticed that the order of conftest.py hooks changes depending on whether or not test files are passed as CLI arguments to pytest.

For example, considering the following directory structure:

.
├── README.md
├── requirements.txt
└── tests
    ├── conftest.py
    ├── nested
    │   ├── conftest.py
    │   └── test_nested.py
    └── test_outer.py

Running python -m pytest runs the outer conftest hooks first followed by the nested conftest hooks.

But if I specify the test files with python -m pytest tests/test_outer.py tests/nested/test_nested.py then I see that the inner conftest runs before the outer conftest.

Here's a more complete demonstration of this: https://github.com/scott-codecov/pytest-order-demo

Is there a way to control this ordering such that it's deterministic regardless of whether pytest is collecting the test files vs. specifying them explicitly?

[ChVeen]

Hi @scott-codecov,

in fact there is a little mechanism to control the ordering by using @pytest.hookimpl(tryfirst=True) or @pytest.hookimpl(trylast=True).
This mechanism is explained at https://docs.pytest.org/en/7.4.x/how-to/writing_hook_functions.html#hook-function-ordering-call-example.
For your code it would look like:

import pytest

@pytest.hookimpl(tryfirst=True)
def pytest_configure():
    print("OUTER")

and

import pytest

@pytest.hookimpl(trylast=True)
def pytest_configure():
    print("INNER")

Then your order is always the same: first OUTER then INNER.