pytest parameter matrices
A few months ago I explained how I efficiently test Django forms with pytest parameterization. Last week, I learned a new trick from Raphael Pierzina’s post about ids for fixtures and parametrize, which is:
You you can add multiple parametrization markers to a test function which then create a test parameter matrix.
The list of test cases can thus be written much more clearly. Compare the example code from my previous post:
from django import forms
import pytest
class ExampleForm(forms.Form):
name = forms.CharField(required=True)
age = forms.IntegerField(min_value=18)
@pytest.mark.parametrize(
'name, age, validity',
[('Hugo', 18, True),
('Egon', 17, False),
('Balder', None, False),
('', 18, False),
(None, 18, False),
])
def test_example_form(name, age, validity):
form = ExampleForm(data={
'name': name,
'age': age,
})
assert form.is_valid() is validity
to the same test using multiple parameterization markers:
@pytest.mark.parametrize(
'name, valid_name',
[
('Hugo', True),
('', False),
(None, False),
]
)
@pytest.mark.parametrize(
'age, valid_age',
[
('18', True),
('17', False),
(None, False),
]
)
def test_example_form(name, age, valid_name, valid_age):
form = ExampleForm(data={
'name': name,
'age': age,
})
assert form.is_valid() is (valid_name and valid_age)
This tests all 9 possible combinations of the three test cases each for name and age. Maybe that’s overkill, but on the other hand I can be sure that I touch all the relevant combinations.
Take note of the last line that checks that the form only validates when both input parameters are valid.
The main advantage I see is legibility. For each form field, I only have to understand the list of test parameters for exactly that field, and not any additional combinations with other fields.
I’m loving it!
Categories: #Tech Tags: #Pytest #Django #Parametrization #Testing