public void CreateOrFindRoleTest()
        {
            var role = database.Roles.SingleOrDefault(r => r.RoleEnum == AppRoleEnum.TestOnly);

            if (role != null)
            {
                database.Roles.Remove(role);
                database.SaveChanges();
            }
            var helperRole = helper.CreateOrFindRole(AppRoleEnum.TestOnly);

            if (helperRole == null)
            {
                Assert.Fail("未返回Role对象。");
            }
            if (helperRole.RoleEnum != AppRoleEnum.TestOnly || helperRole.Name != AppRoleEnum.TestOnly.ToString())
            {
                Assert.Fail("返回的Role对象不符合标准。");
            }
            role = database.Roles.SingleOrDefault(r => r.RoleEnum == AppRoleEnum.TestOnly);
            if (role == null)
            {
                Assert.Fail("Role对象未插入数据库。");
            }
            database.Roles.Remove(role);
            database.SaveChanges();
        }