TST: Use explicit style in all image_comparison calls by QuLogic · Pull Request #31148 · matplotlib/matplotlib

QuLogic · 2026-02-13T07:45:00Z

PR summary

This makes it so that future tests must use the new style (or explicitly opt in to the old), and in the future, we may return to a default of that one instead.

I used a libcst transform to add the kwarg in alphabetical order, so some bits of the diff might be suboptimal in their succinctness, but they should be all consistent.

Fixes #24716

This is based on #31137.

PR checklist

"closes #0000" is in the body of the PR description to link the related issue
new and changed code is tested
[n/a] Plotting related features are demonstrated in an example
[n/a] New Features and API Changes are noted with a directive and release note
[n/a] Documentation complies with general and docstring guidelines

timhoffm · 2026-02-15T21:42:53Z

lib/matplotlib/tests/test_agg.py


-@image_comparison(['agg_filter.png'], remove_text=True)
+@image_comparison(['agg_filter.png'], remove_text=True,
+                  style=('classic', '_classic_test_patch'))


Should we create a new style _classic_test? This feels overly verbose.

I'm not sure that we have a way to create a kind of inheritance that would work like that. If we made a completely new one, we'd be duplicating most of classic with the 2 or 3 lines of _classic_test_patch differing.

Could we dynamically create _classic_test.mplstyle by merging the two files at test startup? Or check it in and write a test that it's just the merge of the two?

Yes, the former seems quite plausible.

@QuLogic I thought about how to document this for debugging (=I want to manually create the same image as in a test). We basically have to state: When running manually, use ('classic', '_classic_test_patch') instead of '_classic_test'.

That brought me to the idea that instead of doing magic at test setup, we could alternatively rewrite the value '_classic_test' to ('classic', '_classic_test_patch'). Not sure which one is better.

There's more than just the style; we do a few other things as part of test setup:

matplotlib/lib/matplotlib/testing/__init__.py

Lines 30 to 52 in cb63559

def setup():

# The baseline images are created in this locale, so we should use

# it during all of the tests.

try:

locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')

except locale.Error:

try:

locale.setlocale(locale.LC_ALL, 'English_United States.1252')

except locale.Error:

_log.warning(

"Could not set locale to English/United States. "

"Some date-related tests may fail.")

mpl.use('Agg')

with _api.suppress_matplotlib_deprecation_warning():

mpl.rcdefaults() # Start with all defaults

# These settings *must* be hardcoded for running the comparison tests and

# are not necessarily the default values as specified in rcsetup.py.

set_font_settings_for_testing()

set_reproducibility_for_testing()

The best way to create a test image is by running an image_comparison and looking at the result image.

QuLogic · 2026-03-11T17:04:48Z

Note, I've decided to wait until the text-overhaul branch is merged before updating this one, as it will change a lot of tests to use mpl20.

This makes it so that future tests *must* use the new style (or explicitly opt in to the old), and in the future, we may return to a default of that one instead. As a shortcut, the `_classic_test` style is generated from `classic` and `_classic_test_patch` at test startup. Fixes matplotlib#24716

QuLogic · 2026-04-10T21:04:47Z

Sorry, followup question, is image_comparison public API? Should I write a release note about the style parameter, use our deprecation machinery, or revert that part entirely now that we know all tests have been tagged?

QuLogic added the status: waiting for other PR label Feb 13, 2026

github-actions bot added topic: mplot3d Documentation: devdocs files in doc/devel labels Feb 13, 2026

QuLogic mentioned this pull request Feb 13, 2026

[TST]: Add classic style to all old image tests. #24716

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QuLogic force-pushed the image-comparison-style branch from 5ac6017 to 85a4a72 Compare February 14, 2026 21:22

timhoffm reviewed Feb 15, 2026

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github-actions bot added the status: needs rebase label Feb 18, 2026

dstansby removed the status: waiting for other PR label Feb 18, 2026

QuLogic force-pushed the image-comparison-style branch from 85a4a72 to a18b014 Compare February 25, 2026 07:22

github-actions bot removed topic: mplot3d Documentation: devdocs files in doc/devel status: needs rebase labels Feb 25, 2026

QuLogic force-pushed the image-comparison-style branch from a18b014 to ec3a2df Compare February 25, 2026 07:30

timhoffm approved these changes Feb 25, 2026

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melissawm added the topic: testing label Feb 25, 2026

github-actions bot added the status: needs rebase label Mar 2, 2026

QuLogic force-pushed the image-comparison-style branch from ec3a2df to 3f4bc2c Compare April 10, 2026 19:47

github-actions bot removed the status: needs rebase label Apr 10, 2026

QuLogic force-pushed the image-comparison-style branch from 3f4bc2c to de1e5d8 Compare April 10, 2026 19:58

tacaswell approved these changes Apr 10, 2026

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QuLogic added this to the v3.11.0 milestone Apr 10, 2026

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TST: Use explicit style in all image_comparison calls#31148

TST: Use explicit style in all image_comparison calls#31148
QuLogic wants to merge 1 commit intomatplotlib:mainfrom
QuLogic:image-comparison-style

QuLogic commented Feb 13, 2026

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	def setup():
	# The baseline images are created in this locale, so we should use
	# it during all of the tests.

	try:
	locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
	except locale.Error:
	try:
	locale.setlocale(locale.LC_ALL, 'English_United States.1252')
	except locale.Error:
	_log.warning(
	"Could not set locale to English/United States. "
	"Some date-related tests may fail.")

	mpl.use('Agg')

	with _api.suppress_matplotlib_deprecation_warning():
	mpl.rcdefaults() # Start with all defaults

	# These settings must be hardcoded for running the comparison tests and
	# are not necessarily the default values as specified in rcsetup.py.
	set_font_settings_for_testing()
	set_reproducibility_for_testing()

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QuLogic commented Feb 13, 2026

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QuLogic commented Mar 11, 2026

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QuLogic commented Apr 10, 2026

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