在WebApi中对WebApi控制器进行单元测试

Question

I am trying to unit test my controller, but as soon as this controller uses its embedded UrlHelper object, it throws an ArgumentNullException .

The action I'm trying to test is this one:

    public HttpResponseMessage PostCommandes(Commandes commandes)
    {
        if (this.ModelState.IsValid)
        {
            this.db.AddCommande(commandes);

            HttpResponseMessage response = this.Request.CreateResponse(HttpStatusCode.Created, commandes);

            // this returns null from the test project
            string link = this.Url.Link(
                "DefaultApi",
                new
                {
                    id = commandes.Commande_id
                });
            var uri = new Uri(link);
            response.Headers.Location = uri;

            return response;
        }
        else
        {
            return this.Request.CreateResponse(HttpStatusCode.BadRequest);
        }
    }

My test method looks like this:

    [Fact]
    public void Controller_insert_stores_new_item()
    {
        // arrange
        bool isInserted = false;
        Commandes item = new Commandes() { Commande_id = 123 };
        this.fakeContainer.AddCommande = (c) =>
            {
                isInserted = true;
            };
        TestsBoostrappers.SetupControllerForTests(this.controller, ControllerName, HttpMethod.Post);

        // act
        HttpResponseMessage result = this.controller.PostCommandes(item);

        // assert
        result.IsSuccessStatusCode.Should().BeTrue("because the storage method should return a successful HTTP code");
        isInserted.Should().BeTrue("because the controller should have called the underlying storage engine");

        // cleanup
        this.fakeContainer.AddCommande = null;
    }

And the SetupControllerForTests method is this one, as seen here :

    public static void SetupControllerForTests(ApiController controller, string controllerName, HttpMethod method)
    {
        var request = new HttpRequestMessage(method, string.Format("http://localhost/api/v1/{0}", controllerName));
        var config = new HttpConfiguration();
        var route = WebApiConfig.Register(config).First();
        var routeData = new HttpRouteData(route, new HttpRouteValueDictionary
                                                 {
                                                     {
                                                             "controller",
                                                             controllerName
                                                     }
                                                 });

        controller.ControllerContext = new HttpControllerContext(config, routeData, request);
        controller.Request = request;
        controller.Request.Properties[HttpPropertyKeys.HttpConfigurationKey] = config;
        controller.Request.Properties[HttpPropertyKeys.HttpRouteDataKey] = routeData;
    }

This is a pretty well documented problem for WebApi2, you can read more about it here for instance ("testing link generation"). Basically, it boils down to either setting a custom ApiController.RequestContext , or mocking the controller's Url property.

The problem is that, in my version of WebApi (Nuget packages: Microsoft.AspNet.WebApi 4.0.20710.0 / WebApi.Core.4.0.30506.0), ApiController.RequestContext does not exist, and Moq cannot mock the UrlHelper class, because the method it should mock ( Link ) is not overridable, or something like that (I didn't dwell on it). Because I'm using WebApi 1. But the blog post I based my code on (as well as many other posts) use V1, too. So I don't understand why it doesn't work, and most of all, how I can make it work.

Thank you !

Answer 1

Not sure if the documentation you linked to was updated since your original post but they show an example where they mock up the UrlHelper and also the Link method.

[TestMethod]
public void PostSetsLocationHeader_MockVersion()
{
    // This version uses a mock UrlHelper.

    // Arrange
    ProductsController controller = new ProductsController(repository);
    controller.Request = new HttpRequestMessage();
    controller.Configuration = new HttpConfiguration();

    string locationUrl = "http://location/";

    // Create the mock and set up the Link method, which is used to create the Location header.
    // The mock version returns a fixed string.
    var mockUrlHelper = new Mock<UrlHelper>();
    mockUrlHelper.Setup(x => x.Link(It.IsAny<string>(), It.IsAny<object>())).Returns(locationUrl);
    controller.Url = mockUrlHelper.Object;

    // Act
    Product product = new Product() { Id = 42 };
    var response = controller.Post(product);

    // Assert
    Assert.AreEqual(locationUrl, response.Headers.Location.AbsoluteUri);
}

Answer 2

So, you need to mock UrlHelper.Link method. It can be easily done with Typemock Isolator (test example from given link):

[TestMethod, Isolated]
public void PostSetsLocationHeader_MockVersion()
{
    // This version uses a mock UrlHelper.

    // Arrange
    ProductsController controller = new ProductsController(repository);
    controller.Request = new HttpRequestMessage();
    controller.Configuration = new HttpConfiguration();

    string locationUrl = "http://location/";

    // Create the mock and set up the Link method, which is used to create the Location header.
    // The mock version returns a fixed string.
    var mockUrlHelper = Isolate.Fake.Instance<UrlHelper>();
    Isolate.WhenCalled(() => mockUrlHelper.Link("", null)).WillReturn(locationUrl);
    controller.Url = mockUrlHelper;

    // Act
    Product product = new Product() { Id = 42 };
    var response = controller.Post(product);

    // Assert
    Assert.AreEqual(locationUrl, response.Headers.Location.AbsoluteUri);
}