Currently we only test with the match predicate as inner predicate. See NestedSearchPredicateIT.
Ideally we would test all predicates, including in particular the ID predicate, which I'm not totally sure would work.
In order to do that, we will probably need some abstraction over the inner predicate, similar to what we did with AggregationDescriptor in SingleFieldAggregationBaseIT. That abstraction could also help facting boost tests () and other tests we duplicated everywhere, such as tests around field incompatibility in multi-index searches (org.hibernate.search.integrationtest.backend.tck.search.predicate.MatchSearchPredicateIT#multiFields_withDslConverter_dslConverterEnabled, ...).