Using Fiddler to create VSTS Web Performance Tests

My shop uses Visual Studio 2010 Ultimate Edition for our test framework. Frankly, I spent a few months automating test cases using the coded-UI style of browser automation before I decided that the “Web Performance Test” was better suited to our testing needs.  (I’ll refer to the web performance test as webtest in the rest of this post.)

Our website makes frequent AJAX calls for server-side user entry validation, and frankly, the recorded coded-UI tests would hang in a non-deterministic way. Even though I inserted custom retry logic when entering user values, the framework would hang and cause our team no end of frustration.

VSTS Web Performance Test (*.webtest)

On a happier note, I’ve had a lot of success using the webtest, a type of test built-in to VSTS which works at the http layer rather than through interaction with the web browser. In our case we use the webtest as a functional test to test the server-side code, though we also use sets of them in load tests as well.

That’s a little background on why I use webtests, but I want to comment more about using Fiddler. If you’re not familiar with Fiddler, it’s a free web debugging tool that logs all http and https traffic between your computer and the internet.

Export Fiddler Sessions when Visual Studio Webtest Recorder Can't

We soon discovered to our dismay that when recording our shopping cart wizard using a web performance test inside VSTS, that not all http requests (read AJAX) were captured. But happily Fiddler DOES capture all this traffic, and the bonus is that Fiddler allows you to export recorded sessions in VSTS web performance test (.webtest) format!

 

Screens in Fiddler after Choosing to Export Sessions

 

 

Sometimes we’ll create a hybrid recording, creating a webtest in VSTS. If some of the requests were not captured, we’ll capture the workflow in Fiddler and then export it to webtest.  After adding the Fiddler-exported webtest to our project, we cut/paste the requests we want into our main webtest.

We’ve had much success using Fiddler to help us build out a complete functional test suite of some fairly complex workflows and would have been stymied in doing this without this great tool.