Port more tests files to pytest

[NicolasHug]

Now that we support pytest, we want to remove the use of the unittest module for different test files. We've already ported a lot of tests in previous issues (#3987, #3945, #3956, #3951), and we want to extend this to more files now.

Instructions

I listed the list of files that need to be ported below. If you're interested in working on this issue, please comment below with "I'm working on file X" so that others don't pick the same file as you do. To keep things simple, please only submit one PR per file, and don't pick more than 2 files at once. You can pick more files once your PRs are merged. Before picking a group, make sure it wasn't picked by another contributor first.

Please don't hesitate to ask for guidance and help! Thanks!!

How to port a test to pytest

Porting a test from unittest to pytest is usually fairly straightforward. For a typical example, see https://github.com/pytorch/vision/pull/3907/files:

• take the test methods out of the Tester(unittest.TestCase) class and just declare it as a function. Note: for some files, it might make sense to keep the class structure, and just rename the class as e.g TestBlahBlah:
• Replace @unittest.skipIf with pytest.mark.skipif(cond, reason=...)
• remove any use of self.assertXYZ.
  • Typically assertEqual(a, b) can be replaced by assert a == b when a and b are pure python objects (scalars, tuples, lists), and otherwise we can rely on assert_equal or torch.testing.assert_close (look for other usage of these files in the codebase if needed)
  • self.assertRaises should be replaced with the pytest.raises(Exp, match=...): context manager, as done in https://github.com/pytorch/vision/pull/3907/files. Same for warnings with pytest.warns
  • self.assertTrue should be replaced with a plain assert
• When a function uses for loops to tests multiple parameter values, one should usepytest.mark.parametrize instead, as done e.g. in https://github.com/pytorch/vision/pull/3907/files.
• It may make sense to keep related tests within a single class. Not all groups need a dedicated class though, it's on a case-by-case basis.

---

Files that need to be ported:

• test_datasets_video_utils.py Port test_datasets_video_utils.py to pytest #4035
  This one will be quite easy, you'll just need to rename the
  Tester(unittest.TestCase) class into e.g. TestVideo, and change with self.assertWarns(UserWarning): into with pytest.warns(UserWarning):
• test_hub.py Port test_hub.py to pytest #4038
• test_datasets_samplers.py Port test_datasets_samplers.py to pytest #4037
• test_models_detection_anchor_utils.py Port test_models_detection_anchor_utils.py to pytest #4046
• test_models_detection_negative_samples.py Port test_models_detection_negative_samples.py to pytest #4045
• test_models_detection_utils.py port test_models_detection_utils.py to pytest #4036
• test_onnx.py Port test_onnx.py to pytest #4047
• test_transforms_video.py Port tests in test_transforms_video.py to pytest #4040

cc @pmeier

[AnirudhDagar]

I'm working on test_datasets_video_utils.py and test_hub.py.

[DevPranjal]

Hey @NicolasHug, I will try working on test_transforms_video.py.

[vivekkumar7089]

Hi @NicolasHug !! I will work on test_datasets_samplers.py and test_models_detection_anchor_utils.py.

[zhiqwang]

Hey @NicolasHug, I will try working on test_onnx.py and test_models_detection_negative_samples.py.

[AnirudhDagar]

I'll also pickup the only one left test_models_detection_utils.py. Should be quite easy too.

[NicolasHug]

All done! Thank you so much everyone for the blazing fast PRs!!