How to mock Url.Action

Question

Method I'm trying to unit test returns:

return Json(new { ok = true, newurl = Url.Action("Index") });

But this line throws NullReferenceException which is caused by this part of return:

newurl = Url.Action("Index")

I was trying to make something with:

Request.SetupGet(x => x.Url).Returns(// Data here);

with no effects.

Can You suggest me any solution?

Answer 1

Here is how to mock UrlHelper using NSubstitute. It would be very similar with other mocking libraries:

UrlHelper Url { get; set; }

[TestFixtureSetUp]
public void FixtureSetUp()
{
    var routes = new RouteCollection();
    RouteConfig.RegisterRoutes(routes);

    var httpContext = Substitute.For<HttpContextBase>();
    httpContext.Response.ApplyAppPathModifier(Arg.Any<string>())
        .Returns(ctx => ctx.Arg<string>());
    var requestContext = new RequestContext(httpContext, new RouteData());
    Url = new UrlHelper(requestContext, routes);
}

// Pages

[Test]
public void HomePage()
{
    Url.Action("home", "pages").ShouldEqual("/");
}

[Test]
public void PageDetails()
{
    Url.Action("details", "pages", new { slug = "contact" }).ShouldEqual("/pages/contact");
}

Answer 2

If you want to attach a mocked UrlHelper to a real Controller, so that when you call an Action on the Controller, it doesn't crash on the UrlHelper, here's what we did (quick and dirty version):

    public class MyController : Controller
    {
        [HttpPost]
        public ActionResult DoSomething(int inputValue)
        {
            var userName = User.UserName();
            return Json(new {
                redirectUrl = Url.Action("RedirectAction", "RedirectController"),
                isRedirect = true,
            });
        }  
    }

    [Test]
    public void Test1()
    {
        var sb = new StringBuilder();

        var response = Substitute.For<HttpResponseBase>();

        response.When(x => x.Write(Arg.Any<string>())).Do(ctx => sb.Append(ctx.Arg<string>()));

        var httpContext = Substitute.For<HttpContextBase>();

        httpContext.Response.Returns(response);
        httpContext.User.Identity.Name.Returns("TestUser");

        var controller = new MyController();

        controller.ControllerContext = new ControllerContext(httpContext, new RouteData(), myController);
        controller.Url = Substitute.For<UrlHelper>();
        controller.Url.Action(Arg.Any<string>(), Arg.Any<string>()).Returns("anything");

        controller.DoSomething(1);
    }