Racing condition xdist fix

[cvanelteren]

Attempting to set the rng generator explicitly rather than using an integer.

[codecov]

Codecov Report

Attention: Patch coverage is 84.00000% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
ultraplot/tests/conftest.py	82.60%	0 Missing and 4 partials ⚠️

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[cvanelteren]

Resolved intermittent failures in test_contour_legend_with_label and test_contour_legend_without_label when running with pytest -n 2 by implementing process-specific temporary directories for each xdist worker. The issue was caused by multiple parallel processes writing matplotlib image comparison results to the same file paths, leading to "Image files did not match" errors due to file system race conditions.

[Copilot]

Pull Request Overview

This PR addresses race conditions when running matplotlib image comparison tests in parallel by explicitly setting RNG generators and isolating matplotlib state per worker.

• Updated pytest-mpl marker usage and network layout seeding
• Introduced an autouse fixture to isolate temp directories and backends
• Configured per-worker result paths in pytest_configure

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tests/test_1dplots.py	Removed parentheses from @pytest.mark.mpl_image_compare and switched seed to a default_rng instance for network layouts
tests/conftest.py	Added isolate_mpl_testing fixture for per-worker isolation and adjusted pytest_configure to set worker-specific result directories

Comments suppressed due to low confidence (3)

ultraplot/tests/test_1dplots.py:578

• NetworkX layout functions expect an int or RandomState seed; passing a Generator may lead to unexpected behavior. Use seed=SEED or wrap in a RandomState object.

            layout_kw = dict(seed=np.random.default_rng(SEED))

ultraplot/tests/test_1dplots.py:528

• Removing the parentheses might prevent pytest-mpl from applying default tolerances or baselines; consider restoring @pytest.mark.mpl_image_compare() or verifying marker behavior.

@pytest.mark.mpl_image_compare

ultraplot/tests/conftest.py:90

• uplt is not imported in this scope, causing a NameError. Import the appropriate module or use plt instead.

    uplt.close("all")

[cvanelteren]

Note I am not completely sure on the proposed fix here but it cannot hurt.

The three tests that are failing are:

• ultraplot.tests.test_1dplots.test_networks
• ultraplot.tests.test_legend.test_contour_legend_with_label
• ultraplot.tests.test_legend.test_contour_legend_without_label

Not really sure at this moment what is causing the issue. The network one is highly likely to be caused by the rng which may be fixed in the first commit here. The other two are a bit of a mystery to me.

[beckermr]

I doubt the change from a seed to an RNG will help networkx, but we can try it.

[cvanelteren]

Ah damn was still drafting this. Couldn't hurt. Not sure why the last two tests are not working properly. It only happens on python 3.10 with mpl 3.90 I believe.

Not your fault didn't mark it as draft.

[beckermr]

Ah sorry. It made the failures on the other PR worse, so we could back it out and try again if you wanted.

[cvanelteren]

We can leave this in as I think it improved the situation from a robustness standpoint (the tmp folders); the network seed was probable not necessary but was a sanity check on my end and the decorator had to be fixed anyway.

[cvanelteren]

I probed around nx codebase and couldn't directly see how they handled if the seed was an int, hence the generator. In their codebase they immediately called .rand on the object.