@Test
    void testExistingAndNonExistingBackendCausesBothErrorAndResult() {
        BlendingSearcherWrapper searcher = setupFirstAndSecond();
        Query query = new Query("/search?query=banana&search=first,nonesuch,second");

        Result result = new Execution(searcher, Execution.Context.createContextStub()).search(query);
        assertEquals(3, result.getConcreteHitCount());
        assertEquals(300.0, result.hits().get(1).getRelevance().getScore(), delta);
        assertEquals(200.0, result.hits().get(2).getRelevance().getScore(), delta);
        assertEquals(100.0, result.hits().get(3).getRelevance().getScore(), delta);
        assertNotNull(result.hits().getError());
        ErrorMessage e = result.hits().getError();
        //TODO: Do not depend on sources order
        assertEquals("Could not resolve source ref 'nonesuch'. Valid source refs are first, second.",
                e.getDetailedMessage());
    }
Disabled because the document source searcher does not handle being asked for
document sumaries for hits it did not create (it will insert the wrong values).
But are we sure fsearch handles this case correctly?
container-search/src/test/java/com/yahoo/prelude/searcher/test/BlendingSearcherTestCase.java