unittest: make `obj` work more like `Function`/`Class` by bluetech · Pull Request #12089 · pytest-dev/pytest

bluetech · 2024-03-08T10:04:34Z

Previously, the obj of a TestCaseFunction (the unittest plugin item type) was the unbound method. This is unlike regular Class where the obj is a bound method to a fresh instance.

This difference necessitated several special cases in in places outside of the unittest plugin, such as FixtureDef and FixtureRequest, and made things a bit harder to understand.

Instead, match how the python plugin does it, including collecting fixtures from a fresh instance.

The downside is that now this instance for fixture-collection is kept around in memory, but it's the same as Class so nothing new. Users should only initialize stuff in setUp/setUpClass and similar methods, and not in __init__ which is generally off-limits in TestCase subclasses.

I am not sure why there was a difference in the first place, though I will say the previous unittest approach is probably the preferable one, but first let's get consistency.

bluetech · 2024-03-08T10:06:58Z

Did this while looking into #12065.

Tested on some of my own (quite large) unittest+pytest projects, and also pytest-django which uses unittest internally (this required adding a backward compat property, but I will update pytest-django if this merged and we could remove the compat).

nicoddemus

Looks great, thanks!

Left minor comments.

nicoddemus · 2024-03-08T11:08:24Z

src/_pytest/unittest.py

+        # runTest is a special no-op name for unittest, can be used when a dummy
+        # instance is needed.


I don't quite get this comment... "name for unittest" you mean pytest's unittest, or stdlib unittest? Also is this recommending calling runTest to obtain a new dummy instance?

I will update the comment to make it clearer. Also we don't really need the parameter so I'll omit it.

nicoddemus · 2024-03-08T11:09:51Z

src/_pytest/unittest.py

    # to declare that our children do not support funcargs.
    nofuncargs = True

+    def newinstance(self, method_name: str = "runTest"):


I understand we have been using _ to separate words in new methods/functions? Anyway this is murky waters anyway, perhaps you wanted to keep consistency within this class.

This overrides Class.newinstance so needs the same name

nicoddemus · 2024-03-08T11:11:20Z

testing/test_unittest.py

    for obj in gc.get_objects():
-        assert type(obj).__name__ != "TestCaseObjectsShouldBeCleanedUp"
+        if type(obj).__name__ == "TestCaseObjectsShouldBeCleanedUp":
+            assert not hasattr(obj, "an_expensive_obj")


Where does this an_expensive_obj comes from? Perhaps leaving a comment explaining it.

I think it's maybe clearer when reading the entire test?

Previously, the `obj` of a `TestCaseFunction` (the unittest plugin item type) was the unbound method. This is unlike regular `Class` where the `obj` is a bound method to a fresh instance. This difference necessitated several special cases in in places outside of the unittest plugin, such as `FixtureDef` and `FixtureRequest`, and made things a bit harder to understand. Instead, match how the python plugin does it, including collecting fixtures from a fresh instance. The downside is that now this instance for fixture-collection is kept around in memory, but it's the same as `Class` so nothing new. Users should only initialize stuff in `setUp`/`setUpClass` and similar methods, and not in `__init__` which is generally off-limits in `TestCase` subclasses. I am not sure why there was a difference in the first place, though I will say the previous unittest approach is probably the preferable one, but first let's get consistency.

purajit · 2024-05-01T22:52:03Z

Fully understand this change, but this should really have be listed as a breaking change - upgrading pytest caused me to have to track down why collection was failing, and took me a good amount of debugging to find this.

--- In pytest >=8.2.0 the unittest logic has been reworked to work more like a Function/Class, (see pytest-dev/pytest/pull/12089). This has the side-effect that during the collection phase all test are instantiated and given that the __init__ func of TraceTestCase includes required keyword arguments not being fulfilled in the collection phase it errors. This is avoided by setting default values on the __init__ definition so a `TraceTestCase.__init__() ` run during collection phase won't error. pytest changelog: https://docs.pytest.org/en/stable/changelog.html#pytest-8-2-0-2024-04-27

--- In pytest >=8.2.0 the unittest logic has been reworked to work more like a Function/Class, (see pytest-dev/pytest/pull/12089). This has the side-effect that during the collection phase all test are instantiated and given that the __init__ func of TraceTestCase includes required keyword arguments not being fulfilled in the collection phase it errors. This is avoided by setting default values on the __init__ definition so a `TraceTestCase.__init__() ` run during collection phase won't error. pytest changelog: https://docs.pytest.org/en/stable/changelog.html#pytest-8-2-0-2024-04-27 Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com>

…#236) * set default values to avoid errors during collection phase --- In pytest >=8.2.0 the unittest logic has been reworked to work more like a Function/Class, (see pytest-dev/pytest/pull/12089). This has the side-effect that during the collection phase all test are instantiated and given that the __init__ func of TraceTestCase includes required keyword arguments not being fulfilled in the collection phase it errors. This is avoided by setting default values on the __init__ definition so a `TraceTestCase.__init__() ` run during collection phase won't error. pytest changelog: https://docs.pytest.org/en/stable/changelog.html#pytest-8-2-0-2024-04-27 Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> * fix flake8 errors Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> * use single quotes to please flake8 Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> * Use None as default instead of Lists Co-authored-by: Christophe Bedard <bedard.christophe@gmail.com> Signed-off-by: Clara Berendsen <42071084+claraberendsen@users.noreply.github.com> * Manage optional parameters on instantiation Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> --------- Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> Signed-off-by: Clara Berendsen <42071084+claraberendsen@users.noreply.github.com> Co-authored-by: Christophe Bedard <bedard.christophe@gmail.com>

…ros2#236) * set default values to avoid errors during collection phase --- In pytest >=8.2.0 the unittest logic has been reworked to work more like a Function/Class, (see pytest-dev/pytest/pull/12089). This has the side-effect that during the collection phase all test are instantiated and given that the __init__ func of TraceTestCase includes required keyword arguments not being fulfilled in the collection phase it errors. This is avoided by setting default values on the __init__ definition so a `TraceTestCase.__init__() ` run during collection phase won't error. pytest changelog: https://docs.pytest.org/en/stable/changelog.html#pytest-8-2-0-2024-04-27 Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> * fix flake8 errors Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> * use single quotes to please flake8 Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> * Use None as default instead of Lists Co-authored-by: Christophe Bedard <bedard.christophe@gmail.com> Signed-off-by: Clara Berendsen <42071084+claraberendsen@users.noreply.github.com> * Manage optional parameters on instantiation Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> --------- Signed-off-by: claraberendsen <42071084+claraberendsen@users.noreply.github.com> Signed-off-by: Clara Berendsen <42071084+claraberendsen@users.noreply.github.com> Co-authored-by: Christophe Bedard <bedard.christophe@gmail.com>

nicoddemus approved these changes Mar 8, 2024

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bluetech force-pushed the unittest-obj branch from 8769d45 to 1a5e0eb Compare March 8, 2024 12:06

bluetech merged commit 83887c0 into pytest-dev:main Mar 8, 2024

bluetech deleted the unittest-obj branch March 8, 2024 18:50

bluetech mentioned this pull request Mar 9, 2024

python: fix instance handling in static and class method tests #12096

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MartinBraquet mentioned this pull request Apr 30, 2024

v8.2.0 raises Can't instantiate abstract class when a test class implements an abstract class #12275

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bluetech mentioned this pull request May 13, 2024

changelog: document unittest 8.2 change as breaking #12320

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stanislavlevin mentioned this pull request May 29, 2024

More Ruff checks, and make it fix getpelican/pelican#3239

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hongfeng2013 mentioned this pull request May 30, 2024

With pytest8.2.0 or later, test cases under test/distributed/ execute will meet issue "object has no attribute 'runTest'. Did you mean: 'run_test'" pytorch/pytorch#127517

Open

The-Compiler mentioned this pull request Jun 10, 2024

pytest 8.2.0 calls @propertys during unittest collection #12446

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Liam-DeVoe mentioned this pull request Feb 7, 2025

Initial support for stateful testing Zac-HD/hypofuzz#51

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The-Compiler mentioned this pull request Jun 26, 2025

Incomplete abstract class no longer logs an error #13546

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claraberendsen mentioned this pull request Feb 25, 2026

Set default values on TraceTestCase to avoid errors on >=8.2.0 pytest ros2/ros2_tracing#236

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unittest: make `obj` work more like `Function`/`Class`#12089

unittest: make `obj` work more like `Function`/`Class`#12089
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		# runTest is a special no-op name for unittest, can be used when a dummy
		# instance is needed.

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