Bug report

Bug description:

The test test_zstd_multithread_compress is always skipped, even when it should be run.

This comes from SUPPORT_MULTITHREADING being initiated to False when the @unittest.skipIf decorator is called. It is changed to True in the global setUp afterwards, but it's too late.

Tested on 3.14.0b3 tag:

$ ./python -c 'from compression.zstd import *; print(CompressionParameter.nb_workers.bounds() != (0, 0))'
True
$ ./python -m test.test_zstd -k test_zstd_multithread_compress -v
test_zstd_multithread_compress (__main__.CompressorTestCase.test_zstd_multithread_compress) ... skipped "zstd build doesn't support multi-threaded compression"

----------------------------------------------------------------------
Ran 1 test in 0.061s

OK (skipped=1)

I'm opening this ticket instead of creating a PR because I don't know why the global SUPPORT_MULTITHREADING was introduced in the test. Maybe to handle when CPython is build without zstd support?

Introduced in gh-132983 @emmatyping

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-136315: Fix skipped multithreading test in test_zstd #136320
• [3.14] gh-136315: Fix skipped multithreading test in test_zstd (GH-136320) #136322