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test: Pre-compile common wheels in base test env#13715

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ichard26 merged 1 commit intopypa:mainfrom
ichard26:test/precompile-common-wheels
Dec 21, 2025
Merged

test: Pre-compile common wheels in base test env#13715
ichard26 merged 1 commit intopypa:mainfrom
ichard26:test/precompile-common-wheels

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@ichard26 ichard26 commented Dec 21, 2025

The test suite disables Python bytecode caching so if we don't pre-compile the bytecode for coverage, setuptools, and pytest-subket which are all preinstalled in the test environments, we pay a heavy import time penalty (e.g., setuptools during a PEP 517 build). pip is already pre-compiled FWIW.

This is doubly bad for coverage and pytest-subket since they are imported on every Python process startup.

Locally, this shaves a full minute from a full test suite run down to 2:45 from 3:45.

Towards #13707.


Another idea I have is to stop copying the test data for every test that requests it. This will need some work since AFAIU some tests depend on being to write freely to the temporary test data folder, but there's no reason why they can't use the normal temporary directory pytest provides. This will hopefully partially alleviate the issues we have with abysmal file I/O performance on Windows.

The test suite disables Python bytecode caching so if we don't
pre-compile the bytecode for coverage, setuptools, and pytest-subket
which are all preinstalled in the test environments, we pay a heavy
import time penalty (e.g., setuptools during a PEP 517 build). pip is
already pre-compiled, FWIW.

This is doubly bad for coverage and pytest-subket since they are
imported on every Python process startup.

Locally, this shaves a full minute from a full test suite run down to
2:45 from 3:45.
@ichard26 ichard26 added C: tests Testing and related things skip news Does not need a NEWS file entry (eg: trivial changes) labels Dec 21, 2025
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Since the individual job times are highly variable, I've taken to use the total billing minutes as a way to determine whether we're saving time in aggregate or not. This PR is at 3 hours and 15 minutes. This is an improvement from:

For reference, this scheduled CI run on main from Nov 23 is at 4 hours and 8 minutes and this scheduled run from Jun 29 is at 3 hours and 21 minutes.

So, it looks like we still have some progress to make. I do wonder what made our test suite so much slower all of a sudden. Probably the removal of legacy builds, but I would have do some testing.

@ichard26 ichard26 merged commit ee5b186 into pypa:main Dec 21, 2025
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@ichard26 ichard26 deleted the test/precompile-common-wheels branch December 21, 2025 20:30
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