Rickard Nilsson

In the following example I will show how easy it is to isolate your client code from ASP.NET code, using the Moles Isolation Framework, in order to test that your code performs as intended.

The example should not be seen as an encouragement to use bad design. On the contrary, I urge you to use Moles to get that ugly, old legacy code you’ve got, and put it under test such that you will have the freedom to rip it apart and improve it.

Prerequisites

1. Download and install Moles Isolation Framework for .NET
2. Open your Solution
3. Create a test project by doing File > Add > New project > Test > Test Project
4. Add the following references
   1. Microsoft.Moles.Framework
      %MolesPath%\PublicAssemblies\Microsoft.Moles.Framework.dll
   2. System.Web
5. On the test project: choose Add > New Item…
6. Choose the Moles template “Moles and Stubs for Testing”
7. Name it “System.Web.moles”

Now Moles will generate an assembly with mocks and stubs of the target assembly (System.Web) and add it to the test project. Your references should look like this:

Class under test

Now you are ready to start writing tests. First we take a look at our sample application. It is a simple ASPX-page which calls Server.MapPath() in the Page_Load method:

In our unit test we want to be able to replace the call to Server.MapPath() such that

1. We won’t get an NullReferenceException
2. We can control what is returned

The following test method will fake the call to Server.MapPath() and assert that it was actually called by the method under test:

Under the covers

To accomplish this we need to understand what is going on. “Server” is an instance property on the System.Web.UI.Page class which eventually will invoke the HttpContext.Current.Server property. Thus, to fake the method call we need to fake several things:

1. Static property HttpContext.Current
2. Instance property Server on HttpContext
3. Instance method MapPath on HttpServerUtility

Access modifier

Finally, to be able to execute the method under test (Page_Load), we need to change its accessibility from protected to public.

Summary

I've shown how easy it is to get started covering your ASP.NET codebehinds with unit tests utilizing Moles Isolation Framework. Please leave feedback and any questions you might have. Good luck testing!