@Test
    public void testAddTagWhenOriginalTagIsNull() throws Throwable {
      // overwriting the vmCreateSpec tags to empty from non-empty
      vmCreateSpec.setTags(null);

      createdVmTaskEntity = vmDcpBackend.prepareVmCreate(projectId, vmCreateSpec);
      vmId = createdVmTaskEntity.getEntityId();
      entityLockDcpBackend.clearTaskLocks(createdVmTaskEntity);
      vm = vmDcpBackend.findById(vmId);
      int originalSize = vm.getTags().size();
      Tag tag = new Tag("namespace:predicate=value");
      vmDcpBackend.addTag(vm.getId(), tag);
      vm = vmDcpBackend.findById(vm.getId());
      assertThat(vm.getTags().size(), is(1));
      List<String> tagValues =
          vm.getTags().stream().map(t -> t.getValue()).collect(Collectors.toList());
      assertTrue(tagValues.contains(tag.getValue()));
    }
  private static void commonVmAndImageSetup(
      VmDcpBackend vmDcpBackend, NetworkDcpBackend networkDcpBackend) throws Throwable {
    AttachedDiskCreateSpec disk1 =
        new AttachedDiskCreateSpecBuilder().name("disk1").flavor("core-100").bootDisk(true).build();
    AttachedDiskCreateSpec disk2 =
        new AttachedDiskCreateSpecBuilder().name("disk2").flavor("core-200").capacityGb(10).build();

    List<LocalitySpec> affinities = new ArrayList<>();
    affinities.add(new LocalitySpec("disk-id1", "disk"));
    affinities.add(new LocalitySpec("disk-id2", "disk"));

    ImageService.State imageServiceState = new ImageService.State();
    imageServiceState.name = "image-1";
    imageServiceState.state = ImageState.READY;
    imageServiceState.size = 1024L * 1024L;
    imageServiceState.replicationType = ImageReplicationType.EAGER;
    imageServiceState.imageSettings = new ArrayList<>();
    ImageService.State.ImageSetting imageSetting = new ImageService.State.ImageSetting();
    imageSetting.name = "n1";
    imageSetting.defaultValue = "v1";
    imageServiceState.imageSettings.add(imageSetting);
    imageSetting = new ImageService.State.ImageSetting();
    imageSetting.name = "n2";
    imageSetting.defaultValue = "v2";
    imageServiceState.imageSettings.add(imageSetting);

    Operation result = dcpClient.post(ImageServiceFactory.SELF_LINK, imageServiceState);

    createdImageState = result.getBody(ImageService.State.class);

    imageId = ServiceUtils.getIDFromDocumentSelfLink(createdImageState.documentSelfLink);

    vmCreateSpec = new VmCreateSpec();
    vmCreateSpec.setName("test-vm");
    vmCreateSpec.setFlavor("core-100");
    vmCreateSpec.setSourceImageId(imageId);
    vmCreateSpec.setAttachedDisks(ImmutableList.of(disk1, disk2));
    vmCreateSpec.setAffinities(affinities);
    vmCreateSpec.setTags(ImmutableSet.of("value1", "value2"));

    List<String> networks = new ArrayList<>();

    List<String> portGroups = new ArrayList<>();
    portGroups.add("p1");
    NetworkCreateSpec networkCreateSpec = new NetworkCreateSpec();
    networkCreateSpec.setName("n1");
    networkCreateSpec.setPortGroups(portGroups);
    TaskEntity networkTask = networkDcpBackend.createNetwork(networkCreateSpec);
    networks.add(networkTask.getEntityId());

    portGroups = new ArrayList<>();
    portGroups.add("p2");
    networkCreateSpec.setName("n2");
    networkCreateSpec.setPortGroups(portGroups);
    networkTask = networkDcpBackend.createNetwork(networkCreateSpec);
    networks.add(networkTask.getEntityId());

    vmCreateSpec.setNetworks(networks);

    createdVmTaskEntity = vmDcpBackend.prepareVmCreate(projectId, vmCreateSpec);
  }