Using parametrize with PyTest
Recap
In my previous post I showed the function to test the access to the castle based on the powerup of the character. It takes a test for the case that the character has_access and a test to verify the character does not have access without the Super Mushroom. Both the castle and character are set as a fixture in the conftest.py.
Snippet - Fixtures for castle and character
import pytest
...
@pytest.fixture(scope="class")
def castle():
return Castle(CASTLE_NAME)
@pytest.fixture(scope="class")
def character():
return Character(CHARACTER_NAME)
...
Snippet - Tests to validate access to castle.
...
class TestCastleClass:
""" Defines the tests for the Castle class """
...
def test_has_access_true_with_super_mushroom(self, castle, character):
""" Test that has_access returns True for Super Mushroom """
character.powerup = 'Super Mushroom'
assert castle.has_access(character)
def test_has_access_false_without_super_mushroom(self, castle, character):
""" Test that has_access returns False for other powerups """
character.powerup = 'Not a mushroom'
assert not castle.has_access(character)
...
Running this in the console looks like this:
$ pytest -k has_access -v
============================================================ test session starts =============================================================
platform darwin -- Python 3.7.3, pytest-5.2.1, py-1.8.0, pluggy-0.13.0 -- /Users/jitsejan/.local/share/virtualenvs/blog-testing-KMgUXSdn/bin/python3.7m
cachedir: .pytest_cache
rootdir: /Users/jitsejan/code/blog-testing
plugins: mock-1.11.1
collected 17 items / 15 deselected / 2 selected
tests/test_castle_class.py::TestCastleClass::test_has_access_true_with_super_mushroom PASSED [ 50%]
tests/test_castle_class.py::TestCastleClass::test_has_access_false_without_super_mushroom PASSED [100%]
Introducing parametrize
Using parametrize writing tests becomes significantly easier. Instead of writing a test for each combination of parameters I can write one test with a list of different sets of parameters. For each set of parameters the same test case will be executed, hence the two test cases above can be replaced by:
@pytest.mark.parametrize('powerup,has_access', [
("Super Mushroom", True),
("Not a mushroom", False),
], ids=['successful', 'failure-without-super-mushroom'])
def test_has_access_true_with_super_mushroom(self, castle, character, powerup, has_access):
""" Test that has_access returns True for Super Mushroom """
character.powerup = powerup
assert castle.has_access(character) == has_access
Running the same selection of tests again still returns two results but now it is indicated by the ID provided as argument for the parametrize.
$ pytest -k has_access -v
============================================================ test session starts =============================================================
platform darwin -- Python 3.7.3, pytest-5.2.1, py-1.8.0, pluggy-0.13.0 -- /Users/jitsejan/.local/share/virtualenvs/blog-testing-KMgUXSdn/bin/python3.7m
cachedir: .pytest_cache
rootdir: /Users/jitsejan/code/blog-testing
plugins: mock-1.11.1
collected 17 items / 15 deselected / 2 selected
tests/test_castle_class.py::TestCastleClass::test_has_access_true_with_super_mushroom[successful] PASSED [ 50%]
tests/test_castle_class.py::TestCastleClass::test_has_access_true_with_super_mushroom[failure-without-super-mushroom] PASSED [100%]
The other test cases in the repo don't lend themselves to be used for parametrization, but it has helped me to reduce the number of test cases in our data platform repo by half. Give it a try :)