JGilmartin JGilmartin - 2 months ago 17
C# Question

mock HttpContext.Current.Server.MapPath using Moq?

im unit testing my home controller. This test worked fine until I added a new feature which saves images.

The method that’s causing the issue is this below.

public static void SaveStarCarCAPImage(int capID)
{
byte[] capBinary = Motorpoint2011Data.RetrieveCapImageData(capID);

if (capBinary != null)
{
MemoryStream ioStream = new MemoryStream();
ioStream = new MemoryStream(capBinary);

// save the memory stream as an image
// Read in the data but do not close, before using the stream.

using (Stream originalBinaryDataStream = ioStream)
{
var path = HttpContext.Current.Server.MapPath("/StarVehiclesImages");
path = System.IO.Path.Combine(path, capID + ".jpg");
Image image = Image.FromStream(originalBinaryDataStream);
Image resize = image.GetThumbnailImage(500, 375, null, new IntPtr());
resize.Save(path, System.Drawing.Imaging.ImageFormat.Jpeg);
}
}
}


As the call is coming from a unit test, HttpContext.Current is null and throws an exception. After reading about Moq and some of the tutorials about using Moq with sessions, im sure it can be done.

so far this the unit test code have come up with, but the issue is HTTPContext.Current is always null, and still throws the exception.

protected ControllerContext CreateStubControllerContext(Controller controller)
{
var httpContextStub = new Mock<HttpContextBase>
{
DefaultValue = DefaultValue.Mock
};

return new ControllerContext(httpContextStub.Object, new RouteData(), controller);
}

[TestMethod]
public void Index()
{
// Arrange
HomeController controller = new HomeController();
controller.SetFakeControllerContext();

var context = controller.HttpContext;

Mock.Get(context).Setup(s => s.Server.MapPath("/StarVehiclesImages")).Returns("My Path");

// Act
ViewResult result = controller.Index() as ViewResult;

// Assert
HomePageModel model = (HomePageModel)result.Model;
Assert.AreEqual("Welcome to ASP.NET MVC!", model.Message);
Assert.AreEqual(typeof(List<Vehicle>), model.VehicleMakes.GetType());
Assert.IsTrue(model.VehicleMakes.Exists(x => x.Make.Trim().Equals("Ford", StringComparison.OrdinalIgnoreCase)));
}

Answer

HttpContext.Current is something that you should absolutely never use if you ever expect your code to be unit tested. It is a static method which simply returns null if there is no web context which is the case of a unit test and cannot be mocked. So one way to refactor your code would be the following:

public static void SaveStarCarCAPImage(int capID, string path)
{
    byte[] capBinary = Motorpoint2011Data.RetrieveCapImageData(capID, path);

    if (capBinary != null)
    {
        MemoryStream ioStream = new MemoryStream();
        ioStream = new MemoryStream(capBinary);

        // save the memory stream as an image
        // Read in the data but do not close, before using the stream.

        using (Stream originalBinaryDataStream = ioStream)
        {
            path = System.IO.Path.Combine(path, capID + ".jpg");
            Image image = Image.FromStream(originalBinaryDataStream);
            Image resize = image.GetThumbnailImage(500, 375, null, new IntPtr());
            resize.Save(path, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
    }
}

You see, now this method no longer depends on any web context and can be tested in isolation. It will be the responsibility of the caller to pass the correct path.

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