private Chain<Searcher> twoTracingSources() {
        addChained(new Searcher() {
            @Override
            public Result search(Query query, Execution execution) {
                query.trace(SOURCE1, 1);
                return execution.search(query);
            }

        }, SOURCE1);

        addChained(new Searcher() {
            @Override
            public Result search(Query query, Execution execution) {
                query.trace(SOURCE2, 1);
                return execution.search(query);
            }

        }, SOURCE2);

        return new Chain<>("default",
                           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