I've created some unit tests for the control event mask, based on legacy/trac#13805. They check that setting `control_testing_set_global_event_mask` and testing `control_event_is_interesting` the control event mask works as expected. I've also added a compile-time check that the number of events doesn't exceed the capacity of control_event_t.event_mask. I just need the bug number to put the git commit together.