Why are these variables here? - They're not in use. Off with their heads!
Remove pointless filtering of expected test levels in test - the test setup logic guarantees that any feasible test variable combination will have corresponding test levels / or singletons.
Merge up from 'main'.
Introduce smoke test that indirectly checks the validity of the test variable indices passed to a filter. It currently fails!
WIP commit - sorting out filter generation in tests. Needs review.