Valhalla's class preloading added more scenario of possible class circularity issues. Class circularity detection already existed for loading of super-types, but now can also happen when preloading field's classes or in a mix of fields and super-types loading. Those new scenarios have to be tested when multiple threads are concurrently trying to load different classes of the cycle, to verify that successful/failed loads are the expected ones and no deadlock is created.