These two tests stress the Waker internal implementation across threads. See the comments in each file. One checks that all wakes come through correctly when collection occurs in parallel, and the other checks that a final wake that clashes with a collection also comes through okay.

These will probably need adjusting to exercise things properly on another CPU since timing is so sensitive. So if you want to try these, be ready to tweak things until you're comfortable that things have been tested sufficiently on your CPU.