c# - Mocking IPrincipal in ASP.NET Core

Question

I have an ASP.NET MVC Core application that I am writing unit tests for. One of the action methods uses User name for some functionality:

SettingsViewModel svm = _context.MySettings(User.Identity.Name);

which obviously fails in the unit test. I looked around and all suggestions are from .NET 4.5 to mock HttpContext. I am sure there is a better way to do that. I tried to inject IPrincipal, but it threw an error; and I even tried this (out of desperation, I suppose):

public IActionResult Index(IPrincipal principal = null) {
    IPrincipal user = principal ?? User;
    SettingsViewModel svm = _context.MySettings(user.Identity.Name);
    return View(svm);
}

but this threw an error as well. Couldn't find anything in the docs either...

Answer 1

The controller’s User is accessed through the HttpContext of the controller. The latter is stored within the ControllerContext.

The easiest way to set the user is by assigning a different HttpContext with a constructed user. We can use DefaultHttpContext for this purpose, that way we don’t have to mock everything. Then we just use that HttpContext within a controller context and pass that to the controller instance:

var user = new ClaimsPrincipal(new ClaimsIdentity(new Claim[]
{
    new Claim(ClaimTypes.Name, "example name"),
    new Claim(ClaimTypes.NameIdentifier, "1"),
    new Claim("custom-claim", "example claim value"),
}, "mock"));

var controller = new SomeController(dependencies…);
controller.ControllerContext = new ControllerContext()
{
    HttpContext = new DefaultHttpContext() { User = user }
};

When creating your own ClaimsIdentity, make sure to pass an explicit authenticationType to the constructor. This makes sure that IsAuthenticated will work correctly (in case you use that in your code to determine whether a user is authenticated).