@Test public void testGroupHappyPathWithListOfContainers() { Set<TaskModel> taskModels = generateTaskModels(5); List<String> containerIds = new ArrayList<String>() { { add("4"); add("2"); } }; Set<ContainerModel> containers = buildSimpleGrouper().group(taskModels, containerIds); Map<String, ContainerModel> containersMap = new HashMap<>(); for (ContainerModel container : containers) { containersMap.put(container.getId(), container); } assertEquals(2, containers.size()); ContainerModel container0 = containersMap.get("4"); ContainerModel container1 = containersMap.get("2"); assertNotNull(container0); assertNotNull(container1); assertEquals("4", container0.getId()); assertEquals("2", container1.getId()); assertEquals(3, container0.getTasks().size()); assertEquals(2, container1.getTasks().size()); assertTrue(container0.getTasks().containsKey(getTaskName(0))); assertTrue(container0.getTasks().containsKey(getTaskName(2))); assertTrue(container0.getTasks().containsKey(getTaskName(4))); assertTrue(container1.getTasks().containsKey(getTaskName(1))); assertTrue(container1.getTasks().containsKey(getTaskName(3))); }