Adding Tests¶

How to add tests¶

Tin uses pytest and pytest-django to run tests. You can add tests to a new app in one of two ways:

Creating a new file in the app called tests.py
Creating a directory called tests/ and adding files that are prefixed with test_ inside the directory

You can then write a function whose name is prefixed test_, and that will be run as a test. A sample test might look like

def test_addition():
   assert 1+1 == 2

You can then run the tests with python3 manage.py test.

Writing good tests¶

Good tests should test the behavior of a specific view or method, and (ideally) not depend on anything else. For example, say we had this view

def my_view(request):
   # this view is at /hi/
   return redirect("/courses/")

A good test for this view would be

from tin.tests import is_redirect


def test_my_view(client):
    response = client.get("/hi/")
    assert is_redirect(response)

Utilities¶

Tin provides several fixtures to ease the process of writing tests. The most commonly used is the login decorator to login in a django client as a user. It also provides some utility functions for checking the types of requests, like is_redirect and is_login_redirect.

Let’s look at an example using all three

from tin.tests import login, is_redirect, is_login_redirect


def test_redirect(client):
   # client is an anonymous user
   response = client.get(reverse("courses:add"))
   assert is_login_redirect(response)

@login("student")
def test_redirect(client):
   # client is logged in as a student
   response = client.get(reverse("courses:add"))
   assert is_redirect(response)

@login("admin")
def test_redirect(client):
   # client is logged in as an admin
   response = client.get(reverse("courses:add"))
   assert not is_redirect(response)

Tips and Tricks¶

Pytest¶

You can pass arguments to pytest by passing in -- after python3 manage.py test. For example, to see the stdout for all tests, run

python3 manage.py test -- -rP

Or to run specific sets of tests:

# run all tests in this file
python3 manage.py test -- tin/apps/courses/courses/tests.py

# run all tests in this directory
python3 manage.py test -- tin/apps/courses/assignments/tests/

# run test_redirect in courses/tests.py
python3 manage.py test -- tin/apps/courses/courses/tests.py::test_redirect

For more details, check out the pytest documentation.

Implementation Detail

As of the last time this page was updated, python3 manage.py test is a wrapper around the raw pytest executable. As such, you can replace python3 manage.py test -- with just pytest.

Note that this may not stay the same in the future, so if you encounter any problems try using python3 manage.py test as a first step.

Parameterization¶

Make heavy use of pytest.mark.parametrize (docs). Parameterizing tests allows for cleaner debugging when they fail. For example, consider this test case

def test_something():
   for i in (1, 2):
       assert 1+i == 2

When this test fails, it’s difficult to tell at which value of i it failed at. Consider the following instead:

@pytest.mark.parametrize("i", (1, 2))
def test_something(i):
   assert i+1 == 2

Now when this test fails, pytest tells us exactly which value of i it failed at! These can also be arbitrarily nested

@pytest.mark.parametrize("i", range(3))
@pytest.mark.parametrize("j", range(3))
def test_commutative_addition(i, j):
   assert i+j == j+i

Here, test_commutative_addition would be run with values of \(i\) and \(j\) such that \((i,j)\in\{(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), ..., (2, 2)\}\)

Fixtures¶

Finding yourself repeating setup code a lot? Write a pytest fixture to do the setup for you.

For example, if you find yourself needing to create a second student often, you could do something like this

@pytest.fixture
def studentB(django_user_model):
   user = django_user_model.objects.create(username="studentB")
   user.is_student = True
   user.save()
   return user

def test_two_students(studentB):
   # do stuff with studentB
   ...

Note

The django_user_model fixture comes from the pytest-django plugin. Tin also provides some convenience fixtures, see Utilities for more details.

If a fixture only sets up something, and does not return anything, use it with pytest.usefixtures.

@pytest.fixture
def all_assigments_quiz(assignment):
   assignment.is_quiz = True
   assignment.save()

@pytest.usefixtures("all_assigments_quiz")
def test_something(assignment):
   # test something, but now assignment is a quiz
   ...

Implementation Detail

This is actually how login works, it’s simply a wrapper around the admin_login, student_login and teacher_login fixtures.