Migrate test infra to pytest

[ZzEeKkAa]

Apparently pytest was already in dependencies but it was not working. There was no configuration and pytest could not recognize the layout. Now you can both run as file and as a package. Everything works:

pytest ./
pytest --pyargs numba.cuda.tests -v
pytest numba_cuda/numba/cuda/tests/cudapy/test_operator.py

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[ZzEeKkAa]

/ok to test

[kkraus14]

Does everywhere that we're currently using unittest, i.e. https://github.com/NVIDIA/numba-cuda/blob/main/numba_cuda/numba/cuda/testing.py, need to be migrated to use pytest as well?

[ZzEeKkAa]

Does everywhere that we're currently using unittest, i.e. https://github.com/NVIDIA/numba-cuda/blob/main/numba_cuda/numba/cuda/testing.py, need to be migrated to use pytest as well?

pytest supports running Python unittest-based tests out of the box. https://docs.pytest.org/en/stable/how-to/unittest.html . So we don't have to

[ZzEeKkAa]

For some reason wheel-test workflow does not see pytest as an executable, maybe some terminal settings, like user mode shell: bash -l {0}? Logs show that pytest was installed. Conda tests pass so.

UPD: decided to go with python -m pytest way.

[ZzEeKkAa]

/ok to test

[gmarkall]

Thanks for doing this!

I have a concern about running in parallel, because of

numba-cuda/numba_cuda/numba/cuda/testing.py

Lines 17 to 23 in 392fed0

	class CUDATestCase(SerialMixin, TestCase):
	"""
	For tests that use a CUDA device. Test methods in a CUDATestCase must not
	be run out of module order, because the ContextResettingTestCase may reset
	the context and destroy resources used by a normal CUDATestCase if any of
	its tests are run between tests from a CUDATestCase.
	"""

When I run using pytest -n auto all the tests appear to run in parallel, whereas with Numba's runtests / unittest hardly any of the tests run in parallel. However, I was surprised to find this didn't result in segfaults due to the launch of kernels from a context that would have been deleted. One reason I might observe this would be if all the workers run their tests for a class serially, without interspersing tests from other classes in-between. I am wondering if it was only a "feature" of Numba's testing framework that interspersed runs of test methods from different test classes.

Whether or not we can safely run tests in parallel with pytest, I still think this change is a good thing - I notice the pytest serial run completes in about the same amount of time as the Numba runtests / unittest framework's parallel run, so I'll experiment with / investigate pytest parallel runs separately later.

[gmarkall]

I'll experiment with / investigate pytest parallel runs separately later.

Followed up in #350.