Mock a Page Request Lifecycle with TypeMock

Let’s say you’re writing a service like an HttpModule that performs an action against each page that gets served up.  Maybe it does something like move the viewstate to the bottom of the page, update a property on the page, or fudge the control hierarchy a bit.

The thing is, you want to unit test it, but how?  Mocking an HttpContext is hard enough, and many times you end up going down the UI automation road. Ugly.

Enter TypeMock.

A few lines of code, setting up the minimum amount of stuff, and you can mock just enough context to actually get a full page request lifecycle to execute - events and all.  So say your service needs to be called during the page PreInit and you can check the results of whatever you did during Load… here’s what that looks like:

[Test(Description = "Tests an external influence on the page lifecycle.")]
public void MyPageServiceTest()
  Page page = new Page();

  MockObject<HttpBrowserCapabilities> mockBrowser = MockManager.MockObject<HttpBrowserCapabilities>(Constructor.NotMocked);
  mockBrowser.ExpectGetAlways("PreferredRenderingMime", "text/html");
  mockBrowser.ExpectGetAlways("PreferredResponseEncoding", "UTF-8");
  mockBrowser.ExpectGetAlways("PreferredRequestEncoding", "UTF-8");
  mockBrowser.ExpectGetAlways("SupportsMaintainScrollPositionOnPostback", false);

  MockObject<HttpRequest> mockRequest = MockManager.MockObject<HttpRequest>(Constructor.Mocked);
  mockRequest.ExpectGetAlways("FilePath", "/default.aspx");
  mockRequest.ExpectGetAlways("HttpMethod", "GET");
  mockRequest.ExpectGetAlways("Browser", mockBrowser.Object);

  MockObject<HttpResponse> mockResponse = MockManager.MockObject<HttpResponse>(Constructor.Mocked);

  HttpContext mockContext = new HttpContext(mockRequest.Object, mockResponse.Object);

  using (StringWriter stringWriter = new StringWriter())
  using (HtmlTextWriter htmlWriter = new HtmlTextWriter(stringWriter))
    mockBrowser.AlwaysReturn("CreateHtmlTextWriter", htmlWriter);
    page.PreInit +=
      delegate(object sender, EventArgs e)
        // Perform some action
    page.Load +=
      delegate(object sender, EventArgs e)
        // Check/Assert the results of your action

Obviously the majority of this could be wrapped up into a library or something, but I show it here to illustrate that, at least in ASP.NET 2.0, this is all it takes.

(You’ll notice that I’m using the Reflective mocks instead of the Natural mocks that I prefer in TypeMock.  The reason is that I’m mocking a couple of internal things and mocking non-public items requires the Reflective mocks.  By mocking these internal convenience methods, I can greatly reduce the amount of setup for this to run.)