public void CanRetrieveChildren(GroupService<HierarchicalGroup> service, string tenant, string name,
                string childName1, string childName2)
            {
                var group = service.Create(tenant, name);
                var child1 = service.Create(tenant, childName1);
                var child2 = service.Create(tenant, childName2);
                service.AddChildGroup(group.ID, child1.ID);
                service.AddChildGroup(group.ID, child2.ID);
                group = service.Get(group.ID);

                var children = service.GetChildren(group);

                children.ShouldNotBeEmpty();
                children.Count().ShouldBe(2);
            }