How to mock Controller.User using moq

You need to Mock the ControllerContext, HttpContextBase and finally IPrincipal to mock the user property on Controller. Using Moq (v2) something along the following lines should work.

    [TestMethod]
    public void HomeControllerReturnsIndexViewWhenUserIsAdmin() {
        var homeController = new HomeController();

        var userMock = new Mock<IPrincipal>();
        userMock.Expect(p => p.IsInRole("admin")).Returns(true);

        var contextMock = new Mock<HttpContextBase>();
        contextMock.ExpectGet(ctx => ctx.User)
                   .Returns(userMock.Object);

        var controllerContextMock = new Mock<ControllerContext>();
        controllerContextMock.ExpectGet(con => con.HttpContext)
                             .Returns(contextMock.Object);

        homeController.ControllerContext = controllerContextMock.Object;
        var result = homeController.Index();
        userMock.Verify(p => p.IsInRole("admin"));
        Assert.AreEqual(((ViewResult)result).ViewName, "Index");
    }

Testing the behaviour when the user isn't an admin is as simple as changing the expectation set on the userMock object to return false.

When using AspNetCore I could not mock the ControllerContext since I got an exception.

Unsupported expression: m => m.HttpContext
Non-overridable members (here: ActionContext.get_HttpContext) may not be used in setup / verification expressions.

Instead I had to mock the HttpContext and create a ControllerContext and pass the HttpContext object along.

I did find that mocking claims or response/request objects works as well when using this method.

[Test]
public void TestSomeStuff() {
  var name = "some name";

  var httpContext = new Mock<HttpContext>();
  httpContext.Setup(m => m.User.IsInRole("RoleName")).Returns(true);
  httpContext.Setup(m => m.User.FindFirst(ClaimTypes.Name)).Returns(name);

  var context = new ControllerContext(new ActionContext(httpContext.Object, new RouteData(), new ControllerActionDescriptor()));

  var controller = new MyController()
  {
    ControllerContext = context
  };

  var result = controller.Index();
  Assert.That(result, Is.Not.Null);
}

Using Moq version 3.1 (and NUnit):

    [Test]
    public void HomeController_Index_Should_Return_Non_Null_ViewPage()
    {
        // Assign:
        var homeController = new HomeController();

        Mock<ControllerContext> controllerContextMock = new Mock<ControllerContext>();
        controllerContextMock.Setup(
            x => x.HttpContext.User.IsInRole(It.Is<string>(s => s.Equals("admin")))
            ).Returns(true);
        homeController.ControllerContext = controllerContextMock.Object;

        // Act:
        ActionResult index = homeController.Index();

        // Assert:
        Assert.IsNotNull(index);
        // Place other asserts here...
        controllerContextMock.Verify(
            x => x.HttpContext.User.IsInRole(It.Is<string>(s => s.Equals("admin"))),
            Times.Exactly(1),
            "Must check if user is in role 'admin'");
    }

Notice that there is no need to create mock for HttpContext, Moq supports nesting of properties when setting up the test.