@Test
    void multiple_tasks_may_be_scheduled_and_answered_at_the_same_time() throws Exception {
        RemoteTaskFixture fixture = createDefaultFixture();
        communicator.setShouldDeferDistributorClusterStateAcks(true);

        MockTask task1 = fixture.scheduleVersionDependentTaskWithSideEffects();
        MockTask task2 = fixture.scheduleVersionDependentTaskWithSideEffects();

        fixture.processScheduledTask();
        assertFalse(task1.isCompleted());
        assertFalse(task2.isCompleted());

        fixture.sendAllDeferredDistributorClusterStateAcks();

        assertTrue(task1.isCompleted());
        assertTrue(task2.isCompleted());
    }
Class for testing states of all nodes. Will fail in constructor with
debug message on non-expected results.
clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/StateChangeTest.java