private List<String> searchChainIds(Collection<ResolveResult> searchChains) {
        return searchChains.stream().map(r -> r.invocationSpec().searchChainId.stringValue()).toList();
    }
Test for SourceRefResolver.

@author Tony Vaagenes
container-search/src/test/java/com/yahoo/search/federation/sourceref/SourceRefResolverTestCase.java