Unit testing ASP.NET Core 3.1 MVC controller - value cannot be null. (Parameter 'provider')

Question

I've recently started working with .NET Core 3.1 after coming from a .NET background and just trying to get up to speed with Unit Testing an MVC controller in the new framework.

In .NET creating an MVC website used to give the option of adding a Unit Test project whereas Core doesn't; so I have followed some guides and have put this simple test together in MSTest for the HomeController index view.

HomeController.cs:

public class HomeController : Controller
{
    public IActionResult Index()
    {
        return this.View();
    }
}

HomeControllerTests.cs:

[TestMethod]
public void WhenIndexIsExecutedAsyncThenContentShouldBeReturned()
{
    // arrange
    var httpContext = new DefaultHttpContext();
    var controller = new HomeController()
        {
            ControllerContext = new ControllerContext
            {
                HttpContext = httpContext
            }
        };

    var actionContext = new ActionContext
        {
            HttpContext = httpContext
        };

    // act
    var result = controller.Index().ExecuteResultAsync(actionContext);

    // assert
    Assert.IsNotNull(result);
    Assert.IsNull(result.Exception);
}

I get an error:

Value cannot be null. (Parameter 'provider')

And I do not know what is causing the error.

user_1285664 · Answer

For the sake of what I was trying to achieve, i.e. a simple test to return the view with some content (the latter falling into an integration test) this code will suffice for the first test. My implementation was overly complicated on first attempt.

    [TestMethod]
    public void WhenIndexIsExecutedAsyncThenViewShouldNotBeNull()
    {
        // arrange
        var controller = new HomeController();

        // act
        var result = controller.Index() as ViewResult;

        // assert
        Assert.IsNotNull(result);
    }

Unit testing ASP.NET Core 3.1 MVC controller - value cannot be null. (Parameter 'provider')

1 Answers