pytest using fixtures as arguments in parametrize

I would like to use fixtures as arguments of pytest.mark.parametrize or something that would have the same results.

For example:

import pytest
import my_package

@pytest.fixture
def dir1_fixture():
    return '/dir1'

@pytest.fixture
def dir2_fixture():
    return '/dir2'

@pytest.parametrize('dirname, expected', [(dir1_fixture, 'expected1'), (dir2_fixture, 'expected2')]
def test_directory_command(dirname, expected):
    result = my_package.directory_command(dirname)
    assert result == expected

The problem with fixture params is that every param of the fixture will get run every time it's used, but I don't want that. I want to be able to choose which fixtures will get used depending on the test.

If you're on pytest 3.0 or later, I think you should be able to solve this particular scenario by writing a fixture along the lines of:

@pytest.fixture(params=['dir1_fixture', 'dir2_fixture'])
def dirname(request):
    return request.getfixturevalue(request.param)

Docs here: http://doc.pytest.org/en/latest/builtin.html#_pytest.fixtures.FixtureRequest.getfixturevalue

However, you can't use this approach if the fixture you're attempting to dynamically load is parametrized.

Alternatively, you might be able to figure something out with the pytest_generate_tests hook. I haven't been able to bring myself to look into that much, though.

Will was on the right path, you should use request.getfixturevalue to retrieve the fixture.

But you can do it right in the test, which is simpler.

@pytest.mark.parametrize('dirname, expected', [
    ('dir1_fixture', 'expected1'),
    ('dir2_fixture', 'expected2')])
def test_directory_command(dirname, expected, request):
    result = my_package.directory_command(request.getfixturevalue(dirname))
    assert result == expected

Another way is to use lazy-fixture plugin:

@pytest.mark.parametrize('dirname, expected', [
    (pytest.lazy_fixture('dir1_fixture'), 'expected1'),
    (pytest.lazy_fixture('dir2_fixture'), 'expected2')])
def test_directory_command(dirname, expected):
    result = my_package.directory_command(dirname)
    assert result == expected

As for now, my only solution is to create a fixture that returns a dictionary of fixtures.

import pytest
import my_package

@pytest.fixture
def dir1_fixture():
    return '/dir1'

@pytest.fixture
def dir2_fixture():
    return '/dir2'

@pytest.fixture
def dir_fixtures(
    dir1_fixture,
    dir2_fixture
    ):
    return {
        'dir1_fixture': dir1_fixture,
        'dir2_fixture': dir2_fixture
    }

@pytest.mark.parametrize('fixture_name, expected', [('dir1_fixture', 'expected1'), ('dir2_fixture', 'expected2')]
def test_directory_command(dir_fixtures, fixture_name, expected):
    dirname = dir_fixtures[fixture_name]
    result = my_package.directory_command(dirname)
    assert result == expected

Not the best since it does not use a solution built into pytest, but it works for me.

This isn't currently supported by pytest. There is an open feature request for it though: https://github.com/pytest-dev/pytest/issues/349.

DO NOT TRY TO CHANGE FIXTURE PARAMETERS DURING TEST EXECUTION

Invalid example: @pytest.fixture(scope="class", params=other_fixture)

Now I'll explain why it doesn't work:

1. Pytest creates session objects before running the test, containing the parameters with which the test will run. During the execution of the test; you cannot change the parameters

2. If you really want to do this (change the parameters dynamically), you can use an intermediate text file: "params.txt". Example: @pytest.fixture(scope="class", params=json.load(open("topics.txt"))). Again, you will not be able to change the content of the file during the test; because if you change it; will not be visible in the test. To do this; we need to change the contents of the file when the program starts and before the session objects are created. To do that; define a method pytest_sessionstart(session) in conftest.py where you change the file content.

3. For more details; check this documentation: https://stackoverflow.com/questions/17801300/how-to-run-a-method-before-all-tests-in-all-classes and https://docs.pytest.org/en/6.2.x/reference.html#pytest.hookspec.pytest_sessionstart