René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Add a check in check_figures_equal that the test did not accidentally plot on non-fixture figures","articleBody":"\u003c!--\r\nWelcome! Thanks for thinking of a way to improve Matplotlib.\r\n\r\n\r\nBefore creating a new feature request please search the issues for relevant feature requests.\r\n--\u003e\r\n\r\n### Problem\r\n\r\n`check_figures_equal` relies on the test plotting onto `fig_test` and `fig_ref`, not elsewhere (e.g. on newly instantiated figures, as noticed in #18579).\r\n\r\n### Proposed Solution\r\n\r\nIt should be reasonable to also fail the test if the test function creates new pyplot figures to catch errors as in #18579.\r\n\r\n### Additional context and prior art\r\n\r\nInstead, we could also change `check_figures_equal` to just not pass the two figures in and always expect the test function to create exactly two pyplot figures itself and check these, but then it's a bit arbitrary which figure is the reference and which is the test (although that only really (barely) matters for display purposes in triage_tests.py), and feels a bit dirty (even ignoring the API break, which is as always manageable)...","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2020-09-25T22:55:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/18581/matplotlib/issues/18581"}