@Test
    void testAsyncExecution() {
        // Create a chain
        Chain<Processor> chain = new Chain<>(new CombineData(), new BlockingSplitter(2), new Get6DataItems(), new DataSource());

        // Execute it
        Request request = new Request();
        request.properties().set("appendage", 1);
        Response response = Execution.createRoot(chain, 0, Execution.Environment.createEmpty()).process(request);

        // Verify the result
        assertEquals(6 * 2 - 1, response.data().asList().size());
        assertEquals("first.2, third.2", response.data().get(0).toString());
        assertEquals("second.2", response.data().get(1).toString());
        assertEquals("first.3", response.data().get(2).toString());
        assertEquals("second.3", response.data().get(3).toString());
        assertEquals("third.3", response.data().get(4).toString());
        // from the parallel execution
        assertEquals("first.2", response.data().get(5).toString());
        assertEquals("second.2", response.data().get(6).toString());
        assertEquals("third.2", response.data().get(7).toString());
        assertEquals("first.3", response.data().get(8).toString());
        assertEquals("second.3", response.data().get(9).toString());
        assertEquals("third.3", response.data().get(10).toString());
    }
Execute a processing chain which forks off into multiple threads
container-core/src/test/java/com/yahoo/processing/execution/test/AsyncExecutionTestCase.java