Mocking WebResponse's from a WebRequest

Question

I have finally started messing around with creating some apps that work with RESTful web interfaces, however, I am concerned that I am hammering their servers every time I hit F5 to run a series of tests..

Basically, I need to get a series of web responses so I can test I am parsing the varying responses correctly, rather than hit their servers every time, I thought I could do this once, save the XML and then work locally.

However, I don't see how I can "mock" a WebResponse, since (AFAIK) they can only be instantiated by WebRequest.GetResponse

How do you guys go about mocking this sort of thing? Do you? I just really don't like the fact I am hammering their servers :S I dont want to change the code too much, but I expect there is a elegant way of doing this..

Update Following Accept

Will's answer was the slap in the face I needed, I knew I was missing a fundamental point!

• Create an Interface that will return a proxy object which represents the XML.
• Implement the interface twice, on that uses WebRequest, the other that returns static "responses".
• The interface implmentation then either instantiates the return type based on the response, or the static XML.
• You can then pass the required class when testing or at production to the service layer.

Once I have the code knocked up, I'll paste some samples.

Thanks Will :)

Answer 1

You can't. Best thing to do is wrap it in a proxy object, and then mock that. Alternatively, you'd have to use a mock framework that can intercept types that can't be mocked, like TypeMock. But you're talking about bucks, there. Better to do a little wrapping.

---

Apparently you can with a little extra work. Check the highest voted answer here.

Answer 2

Instead of a true "mock", what if you just created a few local web services/methods on your server that return the data you need? Involves a bit more work than setting up a mock or test I imagine, but should be able to give you what you need.

So your WebRequest.GetResponse would call out to something like "http://localhost/mytestservice.aspx" or something similar and that page would respond in whatever fashion you require.

I'm probably missing your requirements or over-simplifying, but that's probably how I would approach it :)

Answer 3

This is not a perfect solution yet it worked for me before and deserves extra care for the simplicity :

HTTPSimulator

Also a typemock example documented in typemock forums:

using System;
using System.IO;
using System.Net;
using NUnit.Framework;
using TypeMock;

namespace MockHttpWebRequest
{
  public class LibraryClass
  {
    public string GetGoogleHomePage()
    {
      HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.google.com");
      HttpWebResponse response = (HttpWebResponse)request.GetResponse();
      using (StreamReader reader = new StreamReader(response.GetResponseStream()))
      {
        return reader.ReadToEnd();
      }
    }
  }

  [TestFixture]
  [VerifyMocks]
  public class UnitTests
  {
    private Stream responseStream = null;
    private const string ExpectedResponseContent = "Content from mocked response.";

    [SetUp]
    public void SetUp()
    {
      System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding();
      byte[] contentAsBytes = encoding.GetBytes(ExpectedResponseContent);
      this.responseStream = new MemoryStream();
      this.responseStream.Write(contentAsBytes, 0, contentAsBytes.Length);
      this.responseStream.Position = 0;
    }

    [TearDown]
    public void TearDown()
    {
      if (responseStream != null)
      {
        responseStream.Dispose();
        responseStream = null;
      }
    }

    [Test(Description = "Mocks a web request using natural mocks.")]
    public void NaturalMocks()
    {
      HttpWebRequest mockRequest = RecorderManager.CreateMockedObject<HttpWebRequest>(Constructor.Mocked);
      HttpWebResponse mockResponse = RecorderManager.CreateMockedObject<HttpWebResponse>(Constructor.Mocked);
      using (RecordExpectations recorder = RecorderManager.StartRecording())
      {
        WebRequest.Create("http://www.google.com");
        recorder.CheckArguments();
        recorder.Return(mockRequest);

        mockRequest.GetResponse();
        recorder.Return(mockResponse);

        mockResponse.GetResponseStream();
        recorder.Return(this.responseStream);
      }

      LibraryClass testObject = new LibraryClass();
      string result = testObject.GetGoogleHomePage();
      Assert.AreEqual(ExpectedResponseContent, result);
    }

    [Test(Description = "Mocks a web request using reflective mocks.")]
    public void ReflectiveMocks()
    {
      Mock<HttpWebRequest> mockRequest = MockManager.Mock<HttpWebRequest>(Constructor.Mocked);
      MockObject<HttpWebResponse> mockResponse = MockManager.MockObject<HttpWebResponse>(Constructor.Mocked);
      mockResponse.ExpectAndReturn("GetResponseStream", this.responseStream);
      mockRequest.ExpectAndReturn("GetResponse", mockResponse.Object);

      LibraryClass testObject = new LibraryClass();
      string result = testObject.GetGoogleHomePage();
      Assert.AreEqual(ExpectedResponseContent, result);
    }
  }
}

Answer 4

I found this question while looking to do exactly the same thing. Couldn't find an answer anywhere, but after a bit more digging found that the .Net Framework has built in support for this.

You can register a factory object with WebRequest.RegisterPrefix which WebRequest.Create will call when using that prefix (or url). The factory object must implement IWebRequestCreate which has a single method Create which returns a WebRequest. Here you can return your mock WebRequest.

I've put some sample code up at http://blog.salamandersoft.co.uk/index.php/2009/10/how-to-mock-httpwebrequest-when-unit-testing/