https://github.com/adamchainz/unittest-parametrize
Parametrize tests within unittest TestCases.
https://github.com/adamchainz/unittest-parametrize
Last synced: 6 months ago
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Parametrize tests within unittest TestCases.
- Host: GitHub
- URL: https://github.com/adamchainz/unittest-parametrize
- Owner: adamchainz
- License: mit
- Created: 2023-03-28T12:44:54.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2024-04-29T21:02:47.000Z (over 1 year ago)
- Last Synced: 2024-05-01T12:54:30.798Z (over 1 year ago)
- Language: Python
- Size: 143 KB
- Stars: 48
- Watchers: 3
- Forks: 3
- Open Issues: 1
-
Metadata Files:
- Readme: README.rst
- Changelog: CHANGELOG.rst
- License: LICENSE
- Code of conduct: .github/CODE_OF_CONDUCT.md
- Security: .github/SECURITY.md
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====================
unittest-parametrize
====================
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Parametrize tests within unittest TestCases.
----
**Testing a Django project?**
Check out my book `Speed Up Your Django Tests `__ which covers loads of recommendations to write faster, more accurate tests.
----
Installation
============
Install with:
.. code-block:: bash
python -m pip install unittest-parametrize
Python 3.9 to 3.13 supported.
Usage
=====
The API mirrors |@pytest.mark.parametrize|__ as much as possible.
(Even the name `parametrize `__ over the slightly more common `parameterize `__ with an extra “e”.
Don’t get caught out by that…)
.. |@pytest.mark.parametrize| replace:: ``@pytest.mark.parametrize``
__ https://docs.pytest.org/en/stable/how-to/parametrize.html#parametrize-basics
There are two steps to parametrize a test case:
1. Use ``ParametrizedTestCase`` in the base classes for your test case.
2. Apply ``@parametrize`` to any test methods for parametrization.
This decorator takes (at least):
* the argument names to parametrize, as comma-separated string
* a list of parameter tuples to create individual tests for
Here’s a basic example:
.. code-block:: python
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class SquareTests(ParametrizedTestCase):
@parametrize(
"x,expected",
[
(1, 1),
(2, 4),
],
)
def test_square(self, x: int, expected: int) -> None:
self.assertEqual(x**2, expected)
``@parametrize`` modifies the class at definition time with Python’s |__init_subclass__ hook|__.
It removes the original test method and creates wrapped copies with individual names.
Thus the parametrization should work regardless of the test runner you use (be it unittest, Django’s test runner, pytest, etc.).
It supports both synchronous and asynchronous test methods.
.. |__init_subclass__ hook| replace:: ``__init_subclass__`` hook
__ https://docs.python.org/3/reference/datamodel.html#object.__init_subclass__
Provide argument names as separate strings
------------------------------------------
You can provide argument names as a sequence of strings instead:
.. code-block:: python
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class SquareTests(ParametrizedTestCase):
@parametrize(
("x", "expected"),
[
(1, 1),
(2, 4),
],
)
def test_square(self, x: int, expected: int) -> None:
self.assertEqual(x**2, expected)
Use ``ParametrizedTestCase`` in your base test case class
---------------------------------------------------------
``ParametrizedTestCase`` does nothing if there aren’t any ``@parametrize``-decorated tests within a class.
Therefore you can include it in your project’s base test case class so that ``@parametrize`` works immediately in all test cases.
For example, within a Django project, you can create a set of project-specific base test case classes extending `those provided by Django `__.
You can do this in a module like ``example.test``, and use the base classes throughout your test suite.
To add ``ParametrizedTestCase`` to all your copies, use it in a custom ``SimpleTestCase`` and then mixin to others using multiple inheritance like so:
.. code-block:: python
from django import test
from unittest_parametrize import ParametrizedTestCase
class SimpleTestCase(ParametrizedTestCase, test.SimpleTestCase):
pass
class TestCase(SimpleTestCase, test.TestCase):
pass
class TransactionTestCase(SimpleTestCase, test.TransactionTestCase):
pass
class LiveServerTestCase(SimpleTestCase, test.LiveServerTestCase):
pass
Custom test name suffixes
-------------------------
By default, test names are extended with an index, starting at zero.
You can see these names when running the tests:
.. code-block:: console
$ python -m unittest t.py -v
test_square_0 (t.SquareTests.test_square_0) ... ok
test_square_1 (t.SquareTests.test_square_1) ... ok
----------------------------------------------------------------------
Ran 2 tests in 0.000s
OK
You can customize these names by passing ``param`` objects, which contain the arguments and an optional ID for the suffix:
.. code-block:: python
from unittest_parametrize import param
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class SquareTests(ParametrizedTestCase):
@parametrize(
"x,expected",
[
param(1, 1, id="one"),
param(2, 4, id="two"),
],
)
def test_square(self, x: int, expected: int) -> None:
self.assertEqual(x**2, expected)
Yielding perhaps more natural names:
.. code-block:: console
$ python -m unittest t.py -v
test_square_one (t.SquareTests.test_square_one) ... ok
test_square_two (t.SquareTests.test_square_two) ... ok
----------------------------------------------------------------------
Ran 2 tests in 0.000s
OK
Parameter IDs should be valid Python identifier suffixes.
Since parameter IDs are optional, you can provide them only for some tests:
.. code-block:: python
from unittest_parametrize import param
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class SquareTests(ParametrizedTestCase):
@parametrize(
"x,expected",
[
param(1, 1),
param(20, 400, id="large"),
],
)
def test_square(self, x: int, expected: int) -> None:
self.assertEqual(x**2, expected)
ID-free ``param``\s fall back to the default index suffixes:
.. code-block:: console
$ python -m unittest t.py -v
test_square_0 (example.SquareTests.test_square_0) ... ok
test_square_large (example.SquareTests.test_square_large) ... ok
----------------------------------------------------------------------
Ran 2 tests in 0.000s
OK
Alternatively, you can provide the id’s separately with the ``ids`` argument:
.. code-block:: python
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class SquareTests(ParametrizedTestCase):
@parametrize(
"x,expected",
[
(1, 1),
(2, 4),
],
ids=["one", "two"],
)
def test_square(self, x: int, expected: int) -> None:
self.assertEqual(x**2, expected)
Use with other test decorators
------------------------------
``@parametrize`` tries to ensure it is the top-most (outermost) decorator.
This limitation exists to ensure that other decorators apply to each parametrized test.
So decorators like ``@mock.patch`` need be beneath ``@parametrize``:
.. code-block:: python
from unittest import mock
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class CarpentryTests(ParametrizedTestCase):
@parametrize(
"nails",
[(11,), (17,)],
)
@mock.patch("example.hammer", autospec=True)
def test_nail_a_board(self, mock_hammer, nails): ...
Also note that due to how ``mock.patch`` always adds positional arguments at the start, the parametrized arguments must come last.
``@parametrize`` always adds parameters as keyword arguments, so you can also use `keyword-only syntax `__ for parametrized arguments:
.. code-block:: python
# ...
def test_nail_a_board(self, mock_hammer, *, nails): ...
Multiple ``@parametrize`` decorators
------------------------------------
``@parametrize`` is not stackable.
To create a cross-product of tests, you can use nested list comprehensions:
.. code-block:: python
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class RocketTests(ParametrizedTestCase):
@parametrize(
"use_ions,hyperdrive_level",
[
(use_ions, hyperdrive_level)
for use_ions in [True, False]
for hyperdrive_level in [0, 1, 2]
],
)
def test_takeoff(self, use_ions, hyperdrive_level) -> None: ...
The above creates 2 * 3 = 6 versions of ``test_takeoff``.
For larger combinations, |itertools.product()|__ may be more readable:
.. |itertools.product()| replace:: ``itertools.product()``
__ https://docs.python.org/3/library/itertools.html#itertools.product
.. code-block:: python
from itertools import product
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
class RocketTests(ParametrizedTestCase):
@parametrize(
"use_ions,hyperdrive_level,nose_colour",
list(
product(
[True, False],
[0, 1, 2],
["red", "yellow"],
)
),
)
def test_takeoff(self, use_ions, hyperdrive_level, nose_colour) -> None: ...
The above creates 2 * 3 * 2 = 12 versions of ``test_takeoff``.
Parametrizing multiple tests in a test case
-------------------------------------------
``@parametrize`` only works as a function decorator, not a class decorator.
To parametrize all tests within a test case, create a separate decorator and apply it to each method:
.. code-block:: python
from unittest_parametrize import parametrize
from unittest_parametrize import ParametrizedTestCase
parametrize_race = parametrize(
"race",
[("Human",), ("Halfling",), ("Dwarf",), ("Elf",)],
)
class StatsTests(ParametrizedTestCase):
@parametrize_race
def test_strength(self, race: str) -> None: ...
@parametrize_race
def test_dexterity(self, race: str) -> None: ...
...
History
=======
When I started writing unit tests, I learned to use `DDT (Data-Driven Tests) `__ for parametrizing tests.
It works, but the docs are a bit thin, and the API a little obscure (what does ``@ddt`` stand for again?).
Later when picking up pytest, I learned to use its `parametrization API `__.
It’s legible and flexible, but it doesn’t work with unittest test cases, which Django’s test tooling provides.
So, until the creation of this package, I was using `parameterized `__ on my (Django) test cases.
This package supports parametrization across multiple test runners, though most of them are “legacy” by now.
I created unittest-parametrize as a smaller alternative to *parameterized*, with these goals:
1. Only support unittest test cases.
For other types of test, you can use pytest’s parametrization.
2. Avoid any custom test runner support.
Modifying the class at definition time means that all test runners will see the tests the same.
3. Use modern Python features like ``__init_subclass__``.
4. Have full type hint coverage.
You shouldn’t find unittest-parametrize a blocker when adopting Mypy with strict mode on.
5. Use the name “parametrize” rather than “parameterize”.
This unification of spelling with pytest should help reduce confusion around the extra “e”.
Thanks to the creators and maintainers of ddt, parameterized, and pytest for their hard work.
Why not subtests?
-----------------
|TestCase.subTest()|__ is unittest’s built-in “parametrization” solution.
You use it in a loop within a single test method:
.. |TestCase.subTest()| replace:: ``TestCase.subTest()``
__ https://docs.python.org/3/library/unittest.html#unittest.TestCase.subTest
.. code-block:: python
from unittest import TestCase
class SquareTests(TestCase):
def test_square(self):
tests = [
(1, 1),
(2, 4),
]
for x, expected in tests:
with self.subTest(x=x):
self.assertEqual(x**2, expected)
This approach crams multiple actual tests into one test method, with several consequences:
* If a subtest fails, it prevents the next subtests from running.
Thus, failures are harder to debug, since each test run can only give you partial information.
* Subtests can leak state.
Without correct isolation, they may not test what they appear to.
* Subtests cannot be reordered by tools that detect state leakage, like `pytest-randomly `__.
* Subtests skew test timings, since the test method runs multiple tests.
* Everything is indented two extra levels for the loop and context manager.
Parametrization avoids all these issues by creating individual test methods.