Run C++ testcases in parallel with pytest-xdist (#101440)
After an investigation, running C++ tests with https://github.com/pytest-dev/pytest-cpp is just slower than running them directly, plain and simple. I'm curious on the exact root cause, but that's a story for another day.
`time build/bin/test_lazy` takes half a minute to run 610 tests on `linux-bionic-cuda11.8-py3.10-gcc7 / test (default, 2, 5, linux.4xlarge.nvidia.gpu)` while `time pytest /var/lib/jenkins/workspace/build/bin/test_lazy -v` takes 20+ minutes on the same runner. This is a very costly price to pay.
The saving grace here is that https://github.com/pytest-dev/pytest-cpp supports pytest-xdist to run tests in parallel with `-n auto`, so `time pytest /var/lib/jenkins/workspace/build/bin/test_lazy -v -n auto` takes only 3 minutes. This is still not as fast as running C++ tests directly, but it's order of magnitude faster than running them sequentially.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101440
Approved by: https://github.com/clee2000
