private Searcher createFederationSearcher() {
        return new FederationSearcher(new FederationConfig(builder), SchemaInfo.empty(), new ComponentRegistry<>());
    }
Test for federation searcher. The searcher is also tested in
com.yahoo.prelude.searcher.test.BlendingSearcherTestCase.

@author Arne Bergene Fossaa
container-search/src/test/java/com/yahoo/search/federation/FederationSearcherTestCase.java