private void doTestDeleteByUserGroup() {
    userGroup = mgr.find(UserGroup.class, userGroup.getKey());
    assertNotNull("UserGroup expected", userGroup);

    List<UserGroupToInvisibleProduct> list = userGroup.getUserGroupToInvisibleProducts();
    assertNotNull(list);
    Assert.assertEquals(1, list.size());

    oldUserGroupToInvisibleProduct =
        mgr.find(UserGroupToInvisibleProduct.class, list.get(0).getKey());
    assertNotNull(oldUserGroupToInvisibleProduct);

    mgr.remove(userGroup);
  }