pytest fixture with argument

Question

It seems it it possible to pass argument to fixtures:

yet, when implementing this minimal example, I get an error.

import pytest

@pytest.fixture
def my_fixture(v):
    print("fixture in")
    yield v+1
    print("fixture out")

@pytest.mark.parametrize("my_fixture",[1], indirect=True)
def test_myfixture(my_fixture):
    print(my_fixture)

@pytest.fixture def my_fixture(v): E fixture 'v' not found

Is anything wrong with the code above ?

(python 3.8.10, pytest-6.2.5)

score 7 · Answer 1 · answered Nov 06 '21 at 19:04

To briefly elaborate on Vince's answer: in general, arguments to fixture functions are interpreted as the names of other fixtures to load before the one being defined. That's why you got the error message fixture 'v' not found: pytest thought that you wanted my_fixture to depend on another fixture called v that doesn't exist.

The request argument is an exception to this general rule. It doesn't refer to another fixture. Instead, it instructs pytest to give the fixture access to the request object, which contains information on the currently running test, e.g. which parameters are being tested (via request.param), which markers the test has (via request.node.get_closest_marker()), etc.

So to make use of indirect parametrization, your fixture needs to (i) accept the request argument and (ii) do something with request.param. For more information, here are the relevant pages in the documentation:

score 4 · Accepted Answer · answered Nov 05 '21 at 11:54

4

This works:

@pytest.fixture
def my_fixture(request):
    print("fixture in")
    yield request.param+1 # difference here !
    print("fixture out")

@pytest.mark.parametrize("my_fixture",[1], indirect=True)
def test_myfixture(my_fixture):
    print(my_fixture)

answered Nov 05 '21 at 11:54

Vince

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From the docs: https://docs.pytest.org/en/latest/example/parametrize.html#apply-indirect-on-particular-arguments – Tzane Nov 05 '21 at 11:56
see also the answer from Kale Kundert for more details – Vince Nov 08 '21 at 12:41

score 1 · Answer 3 · answered Nov 05 '21 at 11:07

There is nothing wrong. Fixtures are used to fix constants to reuse them identically in multiple tests. They don't accept any argument. By the way you can create a pytest.fixture that is a "constant" function:

@pytest.fixture
def my_fixture():
    return lambda x: x+1

And avoid print in fixture (on the final version at least).

pytest fixture with argument

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