Port test/test_transforms.py to pytest

Currently, most tests in test/test_transforms.py rely on unittest.TestCase. Now that we support pytest, we want to remove the use of the unittest module.

For a similar issue see https://github.com/pytorch/vision/issues/3956

Instructions

There are many tests in this file, so I bundled them in multiple related groups below. If you’re interested in working on this issue, please comment below with “I’m working on <group X>, <group Y>, etc…” so that others don’t pick the same tests as you do. Feel free to pick as many groups as you wish, but please don’t submit more than 2 groups per PR in order to keep the reviews manageable. Before picking a group, make sure it wasn’t picked by another contributor first. 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 method out of the Tester(unittest.TestCase) class and just declare it as a function
• 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 which is already used in the file.
  • 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. For example here, the tests in group A could be grouped into a TestToPILImage class, the tests in group N could be in TestPad, etc. Not all groups need a dedicated class though, it’s on a case-by-case basis.

CC @ShrillShrestha and @zhiqwang in case you’re interested in this too 😃

---

Groups:

• Groups A: https://github.com/pytorch/vision/pull/3959

  • test_1_channel_ndarray_to_pil_image
  • test_1_channel_tensor_to_pil_image
  • test_2_channel_ndarray_to_pil_image
  • test_2_channel_tensor_to_pil_image
  • test_2d_ndarray_to_pil_image
  • test_2d_tensor_to_pil_image
  • test_3_channel_ndarray_to_pil_image
  • test_3_channel_tensor_to_pil_image
  • test_4_channel_ndarray_to_pil_image
  • test_4_channel_tensor_to_pil_image
  • test_ndarray_bad_types_to_pil_image
  • test_tensor_bad_types_to_pil_image

• Group B https://github.com/pytorch/vision/pull/3985

  • test_accimage_crop
  • test_accimage_pil_to_tensor
  • test_accimage_resize
  • test_accimage_to_tensor

• Group C https://github.com/pytorch/vision/pull/3984

  • test_affine
  • test_random_affine

• Group D https://github.com/pytorch/vision/pull/3981

  • test_autoaugment
  • test_center_crop
  • test_center_crop_2
  • test_color_jitter

• Group E https://github.com/pytorch/vision/pull/4026

  • test_convert_image_dtype_float_to_float
  • test_convert_image_dtype_float_to_int
  • test_convert_image_dtype_int_to_float
  • test_convert_image_dtype_int_to_int
  • test_convert_image_dtype_int_to_int_consistency

• Group F https://github.com/pytorch/vision/pull/3966

  • test_pil_to_tensor
  • test_to_tensor
  • test_to_tensor_with_other_default_dtypes

• Group G https://github.com/pytorch/vision/pull/3981

  • test_five_crop
  • test_ten_crop
  • test_max_value
  • test_linear_transformation

• Group H https://github.com/pytorch/vision/pull/3964

  • test_random_apply
  • test_random_choice
  • test_random_order

• Group I https://github.com/pytorch/vision/pull/3972

  • test_random_crop
  • test_random_erasing
  • test_random_rotation
  • test_randomperspective
  • test_randomperspective_fill

• Group J #3952

  • test_randomresized_params
  • test_resize

• Group K https://github.com/pytorch/vision/pull/3957

  • test_rotate
  • test_rotate_fill
  • test_gaussian_blur_asserts
  • test_lambda

• Group L https://github.com/pytorch/vision/pull/3971

  • test_random_horizontal_flip
  • test_random_vertical_flip
  • test_normalize
  • test_normalize_3d_tensor
  • test_normalize_different_dtype

• Group M https://github.com/pytorch/vision/pull/3962

  • test_to_grayscale
  • test_random_grayscale

• Group N #3954

  • test_pad
  • test_pad_raises_with_invalid_pad_sequence_len
  • test_pad_with_mode_F_images
  • test_pad_with_non_constant_padding_modes
  • test_pad_with_tuple_of_pad_values

• Group O https://github.com/pytorch/vision/pull/3955

  • test_random_invert
  • test_random_posterize
  • test_random_solarize
  • test_random_adjust_sharpness
  • test_random_autocontrast
  • test_random_equalize

• Group P #3950

  • test_adjust_brightness
  • test_adjust_contrast
  • test_adjust_gamma
  • test_adjust_hue
  • test_adjust_saturation
  • test_adjust_sharpness
  • test_adjusts_L_mode

cc @pmeier

[NicolasHug]

All done! Thank you so much everyone for your help!!

[pmeier]

@NicolasHug I can help review. Just ping me.