pytest.mark.parametrize with django.test.SimpleTestCase

Question

I am using pytest 3.2.2 and Django 1.11.5 on Python 3.6.2 on Windows.

The following code

import django.test
import pytest

class ParametrizeTest:
    @pytest.mark.parametrize("param", ["a", "b"])
    def test_pytest(self, param):
        print(param)
        assert False

works as expected:

scratch_test.py::ParametrizeTest::test_pytest[a] FAILED scratch_test.py::ParametrizeTest::test_pytest[b] FAILED

But as soon as I change it to use Django's SimpleTestCase, like this:

class ParametrizeTest(django.test.SimpleTestCase):
   ...

it fails with

TypeError: test_pytest() missing 1 required positional argument: 'param'

Can anybody explain why? And what to do against it?
(I actually even need to use django.test.TestCase and access the database.)

I have the following pytest plugins installed:

plugins: random-0.2, mock-1.6.2, django-3.1.2, cov-2.5.1

but turning any one of them (or all of them) off via -p no:random etc. does not help.

Answer 1

The Django test class is a unittest.TestCase subclass. Parametrization is unsupported and this is documented under the section pytest features in unittest.TestCase subclasses:

---

The following pytest features do not work, and probably never will due to different design philosophies:

• Fixtures (except for autouse fixtures)
• Parametrization
• Custom hooks

---

If you need parametrized tests and pytest runner, your best bet is to abandon the unittest style - this means move the setup/teardown into fixtures (pytest-django plugin has already implemented the hard parts for you), and use module level functions for your tests.

Answer 2

Use @pytest.mark.django_db

Thanks, wim, for that helpful answer. RTFM, once again.

For clarity, here is the formulation that will work (equivalent to a test inheriting from TestCase, not just SimpleTestCase). Make sure you have pytest-django installed and then do:

import pytest

@pytest.mark.django_db
class ParametrizeTest:
    @pytest.mark.parametrize("param", ["a", "b"])
    def test_pytest(self, param):
        print(param)
        assert False

(BTW: Funnily, one reason why I originally decided to use pytest was that the idea of using plain test functions instead of test methods appealed to me; I like lightweight approaches.
But now I almost exclusively use test classes and methods anyway, because I prefer the explicit grouping of tests they provide.)