public void CheckFollowerNotExistsTest()
        {
            // act

            _userRepositoryMock.Setup(x => x.GetChildren(It.IsAny<User>())).Returns(new List<User>());
            var userManager = new UserManager(_userRepositoryMock.Object);

            // actual
            userManager.FollowUser(new User(), new User());

            // assert
            _userRepositoryMock.Verify(x => x.AddChild(It.IsAny<User>(), It.IsAny<User>()));
        }
        public void FollowUserTest()
        {
            // act

            _userRepositoryMock.Setup(x => x.AddChild(It.IsAny<User>(), It.IsAny<User>()));
            var userManager = new UserManager(_userRepositoryMock.Object);

            // actual
            userManager.FollowUser(new User(), new User());

            // assert
            _userRepositoryMock.Verify(x => x.AddChild(It.IsAny<User>(), It.IsAny<User>()));
        }