This takes 10 seconds or more, while other allocation tests are almost instantaneous. Can we simplify this? It looks like it tries to do a basic allocation (5 shards, 1 replica) of a new index when a ton of indexes already exist on just 4 nodes. Perhaps we could test similar circumstances without thousands of shards? Alternatively, we could just make this an integration test (leave the impl, but rename to IT). It doesn't really seem like a unit test as it is now.

Also, as a side note, this test is the only user of CatAllocationTestCase. Perhaps we can also eliminate this abstraction and just test directly (eliminating the zipped shard state)? @s1monw do you have any thoughts here?