private Map<String, List<String>> createClusters() {
        return Map.of("clusterOne", List.of("one", "two"),
                "clusterTwo", List.of("one", "three"));
    }
Tests using synthetic index names for IndexFacts class.

@author Steinar Knutsen
container-search/src/test/java/com/yahoo/prelude/test/IndexFactsTestCase.java