From T231358, 062e067d4964c2854c33821fb5522cf578dc4f89 for MinervaNeue made a ResourceLoaderImageModule invalid since it has an image pointing to a non existent file:
+ "userSandbox": "resources/resources/skins.minerva.personalMenu.icons/userSandbox.svg" ^^^^^^^^^^^^^^^^^^^ - "userSandbox": "resources/skins.minerva.mainMenu.icons/userSandbox.svg"
MediaWiki has structure tests to validate resources file existence but it does not have any such tests for ResourceLoaderImageModule ones.
tests/phpunit/structure/ResourcesTest.php only look for modules being an instance of ResourceLoaderFileModule, while ResourceLoaderImageModule descend directly from ResourceLoaderModule.
We thus need an extra structure test in ResourcesTest.php to validate that images referred to by a ResourceLoaderImageModule are actually existing.