Use pytest.mark.parametrize both directly and indirectly

July 12, 2023

Using pytest, how can I parametrise a test function and then use the value both directly and indirectly?

For example, take the very basic test below to check that a function to square a number returns the correct value. As far as I know, I have to parameterise the test function with the same set of arguments twice – once directly and once indirectly.

However, because pytest runs all possible combinations of parameters, this means that the test function fill pass twice (1-1 and 2-2) and fail twice (1-2 and 2-1).

Is there a way to see the parameter value passed to the square_number fixture in the test function as well?

Example code

import pytest

def calculate_square(num: int):
    return num ** 2

args = [1,2]

@pytest.mark.parametrize('number', args)
class TestSomething:

    @pytest.fixture(scope='module')
    def square_number(self, request):
        yield calculate_square(request.param)

    @pytest.mark.parametrize('square_number', args, indirect=True)
    def test_first_thing(self, number, square_number):
        assert number ** 2 == square_number

Example code results

q.py::TestSomething::test_first_thing[1-1] PASSED
q.py::TestSomething::test_first_thing[1-2] FAILED
q.py::TestSomething::test_first_thing[2-1] FAILED
q.py::TestSomething::test_first_thing[2-2] PASSED

Desired code


    @pytest.mark.parametrize('square_number', args, indirect=True)
    def test_first_thing(self, square_number):
        number = ??? # Somehow get current 'args' value from 'square_number'
        assert number ** 2 == square_number

Desired results

q.py::TestSomething::test_first_thing[1] PASSED
q.py::TestSomething::test_first_thing[2] PASSED

>Solution :

Unless I’m missing something here, why do you need indirect parametrization at all?

import pytest


@pytest.mark.parametrize(
    'number, expected',
    [  # this could be `[(x, x ** 2) for x in (1, 2)]`
        (1, 1),
        (2, 4),
    ],
)
def test_square(number, expected):
    assert number ** 2 == expected

You can of course also return a tuple from the fixture and unpack it:

import pytest


@pytest.fixture()
def square_number(request):
    return (request.param, request.param ** 2)


@pytest.mark.parametrize(
    'square_number',
    [1, 2],
    indirect=True,
)
def test_square(square_number):
    number, expected = square_number
    assert number ** 2 == expected