Should I write unit test for controller or service layer or both of them?

I'm learning and trying use unit test for my project. But when I try write a demo with unit test I saw that unit test for controller same like for service layer. Below is unit test code I wrote for controller and service layer

Controller test:

  private Mock<ICountryService> _countryServiceMock;
  CountryController objController;
  List<Country> listCountry;

  [TestInitialize]
  public void Initialize()
  {

      _countryServiceMock = new Mock<ICountryService>();
      objController = new CountryController(_countryServiceMock.Object);
      listCountry = new List<Country>() {
       new Country() { Id = 1, Name = "US" },
       new Country() { Id = 2, Name = "India" },
       new Country() { Id = 3, Name = "Russia" }
      };
  }

  [TestMethod]
  public void Country_Get_All()
  {
      //Arrange
      _countryServiceMock.Setup(x => x.GetAll()).Returns(listCountry);

      //Act
      var result = ((objController.Index() as ViewResult).Model) as List<Country>;

      //Assert
      Assert.AreEqual(result.Count, 3);
      Assert.AreEqual("US", result[0].Name);
      Assert.AreEqual("India", result[1].Name);
      Assert.AreEqual("Russia", result[2].Name);

  }

Service test:

  private Mock<ICountryRepository> _mockRepository;
  private ICountryService _service;
  Mock<IUnitOfWork> _mockUnitWork;
  List<Country> listCountry;

  [TestInitialize]
  public void Initialize()
  {
      _mockRepository = new Mock<ICountryRepository>();
      _mockUnitWork = new Mock<IUnitOfWork>();
      _service = new CountryService(_mockUnitWork.Object, _mockRepository.Object);
      listCountry = new List<Country>() {
       new Country() { Id = 1, Name = "US" },
       new Country() { Id = 2, Name = "India" },
       new Country() { Id = 3, Name = "Russia" }
      };
  }

  [TestMethod]
  public void Country_Get_All()
  {
      //Arrange
      _mockRepository.Setup(x => x.GetAll()).Returns(listCountry);

      //Act
      List<Country> results = _service.GetAll() as List<Country>;

      //Assert
      Assert.IsNotNull(results);
      Assert.AreEqual(3, results.Count);
  }