ItemCacheTagsTest::testEntityCreation() and ShortcutCacheTagsTest::testEntityCreation() check for cache entries in the render cache even though nothing was cached. This needlessly complicates things as any refactoring of the render cache might inadvertently make these tests fail as shown in #2551419-158: Abstract RenderCache into a separate service that is capable of cache redirects in a non-render array-specific way
The easy fix is to add a new method to the base class that allows you to run a slimmed down version of verifyRenderCache that only runs the basic checks, does not check for redirects and, most importantly, uses the default cache backend.