public async Task AddRolesToUsers()
        {
            // Arrange
            var userId = 3;

            var ids = context
                      .Roles
                      .Where(r => r.RoleLevel != RoleLevel.NULL)
                      .ToList()
                      .Select(r => r.Id)
                      .ToList();

            var userRoleIds = context
                              .Roles
                              .Where(r => r.Users.Any(ur => ur.UserId == userId))
                              .ToList()
                              .Select(r => r.Id)
                              .ToList();

            ids = ids.RemoveSubList(userRoleIds).ToList();

            // Act
            var result = await sut.AddRoles(userId, ids);

            // Assert
            Assert.That(result.Success, Is.True);
        }