@Test
    void testNonexistingBackendsCausesErrorOnFirst() {
        // Feel free to change to include all in the detail message...
        BlendingSearcherWrapper searcher = setupFirstAndSecond();
        Query query = new Query("/search?query=banana&search=nonesuch,orsuch");

        Result result = new Execution(searcher, Execution.Context.createContextStub()).search(query);
        assertEquals(0, result.getConcreteHitCount());
        assertNotNull(result.hits().getError());
        ErrorMessage e = result.hits().getError();
        assertEquals("Invalid query parameter", e.getMessage());
        //TODO: Do not depend on sources order
        assertEquals("4: Invalid query parameter: Could not resolve source ref 'nonesuch'. Could not resolve source ref 'orsuch'. Valid source refs are first, second.",
                e.toString());
    }
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