Friday, December 01, 2006

Unit tests - Web applications


We have had our unit test .NET assemblies up and running through Cruise Control for nearly a year now. This has worked very well in catching bugs early introduced by developers hastily checking in code without ensuring that ALL unit tests execute successfully. We use a main nant target which executes about a dozen testing assembly and any failures send an email to the development group so the whole team can see the user/s responsible for the checkins which broke the build. We name and shame them and this usually gets them, me quite a few times :(, to fix the build promptly.

However over the last year I noticed 90% of the defects we introduced related to the web application e.g. common script errors or simple page errors which should have been caught however because

  1. The quality of testing performed by each developer was minimal
  2. No developer ever regression tested many other potentially effected areas

We usually had a large number of issues which QA found come each major release. It was then a battle to fix them AND fix any other defects found from the new changes in the release. We barely had enough bandwidth to fix defects from the new changes let alone issues introduced in other areas. Since then I have had a strong motivation to enable a cruise control project which checks for changes in the web application and runs a unit test assembly with a selection of tests in the web app.

The unit testing of the web application requires a new class I’ve created called InternetExplorerWrapper which provides a number of interesting features

  1. Managed access to the unmanaged internet explorer object to manipulate the object model of page contents when pages are navigated to. E.g. forms and their input fields, frames, anchors, images among many other elements.
  2. Support to create unit test assertion with methods such as AssertFormFieldClassName which assert the class name of a specific form field e.g. used in test which specify a different class for fields which fail validation.
  3. Internal auto reset event objects to ensure methods such as ClickAnchor only return back to the unit test code when the anchor has been clicked and the new page navigated too. The document complete event is used in this case, however this is made tricky because in some cases 3 or 4 document complete events maybe fired together because IE is loading multiple documents for a given request.
  4. Methods to assist with viewing and manipulating the IE object model e.g. outputting the contents HTMLDocument object to the trace window. In this way you can see the elements you can access through your unit tests at specific points in time. Also other methods such as TraceDocsLoaded show you how many events are fired for a given request to help determine how many document complete events to wait for in requests such as ClickAnchor ( c)

There were quite a few details which were problematic e.g. the creation of pop up windows e.g. these need to be wrapped by catching the NewWindow event, then create a new IE wrapper object around this and storing in a hash table within the original requested page. Client code can then access the new windows using methods off the main IE wrapper object such as GetNewIEWindow.

Has anyone else had experience creating unit tests for web applications, I’d be interested to hear your thoughts. The framework should work regardless of the platform used to build the application e.g. ASP / ASP.NET and JSP.

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