Django: Parameterized tests for all model admin classes

Here’s an application of “test smarter, not harder”, as per Luke Plant’s post. I came up with this recently whilst working on my client Silvr’s project, and I’m pretty proud of it. It should apply to any project using Django’s admin.

When you declare a Django ModelAdmin class, the built-in system checks ensure that various attributes are well-defined, using the right data types and values. But they can’t cover everything, because there is so much flexibility. So it’s possible to have, for example, a bad field name in search_fields.

You can ensure that a ModelAdmin class works properly by writing tests to load its various views. But rather than write individual tests, you can “push down the loop”, and write parameterized tests that run on every ModelAdmin.

The below code tests all model admins’ “changelist” and “add” pages. It’s all generic, so you should be able to copy-paste it into most Django projects without modification.

from __future__ import annotations

from collections.abc import Callable
from http import HTTPStatus
from typing import Any

from django.contrib.admin.auth.models import User
from django.contrib.admin.sites import AdminSite
from django.contrib.admin.sites import all_sites
from django.db.models import Model
from django.test import TestCase
from django.urls import reverse
from parameterized import param
from parameterized import parameterized


def name_test(func: Callable[..., Any], param_num: int, param: param) -> str:
    site = param.args[0]
    model_admin = param.args[2]
    return f"{func.__name__}_{site.name}_{str(model_admin).replace('.', '_')}"


each_model_admin = parameterized.expand(
    [
        (site, model, model_admin)
        for site in all_sites
        for model, model_admin in site._registry.items()
    ],
    name_func=name_test,
)


class ModelAdminTests(TestCase):
    user: User

    @classmethod
    def setUpTestData(cls):
        cls.user = User.objects.create_superuser(
            email="admin@example.com", password="test"
        )

    def setUp(self):
        self.client.force_login(self.user)

    def make_url(self, site: AdminSite, model: type[Model], page: str) -> str:
        return reverse(
            f"{site.name}:{model._meta.app_label}_{model._meta.model_name}_{page}"
        )

    @each_model_admin
    def test_changelist(self, site, model, model_admin):
        url = self.make_url(site, model, "changelist")
        response = self.client.get(url, {"q": "example.com"})
        assert response.status_code == HTTPStatus.OK

    @each_model_admin
    def test_add(self, site, model, model_admin):
        url = self.make_url(site, model, "add")
        response = self.client.get(url)
        assert response.status_code in (
            HTTPStatus.OK,
            HTTPStatus.FORBIDDEN,  # some admin classes blanket disallow "add"
        )

Notes:

• The tests use the parameterized package to parameterize the tests. This package works with unittest TestCase classes, like those from Django’s testing framework. (The parameterization also works within pytest.)

• each_model_admin is a test method decorator that expands the test to run on every model admin class, in every admin site. Most projects use a single admin site, the default one, but it’s possible to have multiple sites.

  The definition uses the all_sites weak set which contains all admin site instances. This is an undocumented piece of Django, but stable since its addition in 2017 (perhaps we could document it…).

  The name_test function generates a nice name for each test method, from the parameters.

• ModelAdminTests.setUpTestData creates a superuser for the test. Since superusers have all permissions, they should be able to access all admin pages.

• The two tests, test_changelist and test_add, fetch the respective pages from the ModelAdmin classes. These are the two views that all model admins contain that respond to GET requests and don’t need any pre-populated data.

  The two tests cover many model admin attributes, such as list_display and related methods, or customizations in get_queryset(). test_changelist checks that search_fields is well-defined by adding the q query parameter.

  test_add allows “forbidden” status codes, because sometimes admin classes disallow access to the “add” page. This is done with an overridden has_add_permission():

  class BookAdmin(admin.ModelAdmin):
      ...
  
      def has_add_permission(self, request, obj=None):
          # Read-only
          return False
  

$ pytest example/tests/test_admin.py -vv
======================== test session starts =========================
...

example/tests/test_admin.py::ModelAdminTests::test_add_admin_example_BookAdmin PASSED [  0%]
example/tests/test_admin.py::ModelAdminTests::test_changelist_admin_example_BookAdmin PASSED [  0%]
...

If your Django project’s long test runs bore you, I wrote a book that can help.

One summary email a week, no spam, I pinky promise.

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• Django: How to profile and improve startup time
• Django Settings Patterns to Avoid
• How to implement a “dry run mode” for data imports in Django

Tags: django, python