How to unit test ViewComponent.Invoke()?

Question

In ViewComponent object, HttpContext and User are read-only properties.

How to unit test such a component?

I'm using the MSTest Freamwork.

The follow properties are used in my code

1. Cookie
2. Session
3. User(System.Security.Principal)

---

public ViewViewComponentResult Invoke()
{
    var vm = new SummaryViewModel();
    if (User.Identity is ClaimsIdentity identity && identity.IsAuthenticated)
    {
        vm.IsAuthenticated = true;
        vm.UserName = identity.Claims.FirstOrDefault(c => c.Type == "UserName").Value;
        vm.PhotoUrl = identity.Claims.FirstOrDefault(c => c.Type == "FacePicture").Value;
    }
    return View(vm);
}

[TestMethod]
public void UserSummaryVcTest()
{
    var component = new UserSummaryViewComponent();
    var model = component.Invoke().ViewData.Model as SummaryViewModel;
    Assert.AreEqual("UserName", model.UserName);
} 

Answer 1

According to source code the ViewComponent relies on the ViewComponentContext.ViewContext to expose those read only properties, Which in turn accesses the HttpContext. That is your entry point to mock the desired values.

[TestMethod]
public void UserSummaryVcTest() {

    // Arrange
    var expected = "Username value";
    var httpContext = new DefaultHttpContext(); //You can also Mock this
    //...then set user and other required properties on the httpContext as needed

    var viewContext = new ViewContext();
    viewContext.HttpContext = httpContext;
    var viewComponentContext = new ViewComponentContext();
    viewComponentContext.ViewContext = viewContext;

    var viewComponent = new UserSummaryViewComponent();
    viewComponent.ViewComponentContext = viewComponentContext;

    //Act
    var model = viewComponent.Invoke().ViewData.Model as SummaryViewModel;

    //Assert
    Assert.AreEqual(expected, model.UserName);
}