Overview

https://twitter.com/JoshuaKGoldberg/status/1497766678415003653

Its dynamic test generation generates >15k tests and on my Surface Laptop 4 i7, takes >2 minutes to run. Wowee. In generating timings for #4584 I observed it frequently being a tail end test that prolongs the test run.

We should split it up a bit into separate test files so it's not a bottleneck.