public void AddSubProject_ShouldWork()
        {
            ProjectModel mainProject = new ProjectModel()
            {
                Name     = "Main",
                Priority = ProjectPriority.TOP,
                Status   = ProjectStatus.IN_PROGRESS
            };
            ProjectModel subProject = new ProjectModel()
            {
                Name     = "sub",
                Priority = ProjectPriority.MEDIUM,
                Status   = ProjectStatus.TODO
            };

            mainProject.AddSubProject(subProject);

            Assert.Contains(subProject, mainProject.SubProjects);
            Assert.Contains(mainProject.Id, subProject.ParentIdTreePath);
        }