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Machine Learning : Article

AJAX Testing - Best Practices

Selenium, a potential solution

What’s the Problem? Why Is AJAX Testing So Hard?
The problem with AJAX testing is that there are immediately multiple event streams that can affect the User Interface – first, the user events that we are accustomed to (clicks, drags, typing, drags, drops), and, second, the asynchronous message events (that can have many simultaneous open requests) that are sent to the Web server. The uncertainty about the timing and sequence of the responses to the AJAX message requests introduces a lack of determinism into the testing that the test designer needs to handle properly.

Test validations can fail because the element being tested hasn’t been populated yet by the AJAX response. One solution is to put a pause before the validation, but this is fragile, since the timing of the pause might not be sufficient on a slow machine, while being unnecessarily slow on a faster one. The timing and sequence of message responses can vary widely based on server load and available bandwidth so any test that depends on timing is problematic. Figure 1 provides an example.

In this simple HTTP recording, four requests are sent to the Web server. The messages and packets from the responses are color-coded. As Figure 2, Figure 3, Figure 4, and Figure 5 show, the response packets for Message 2 return to our browser after the responses to Message 3. Testers must deal with this uncertainty in the design of the testing. This is a very simple example. Real world scenarios are more complex.

What About Cross-Browser Testing? Do I Have To?
In June 2004, Microsoft Internet Explorer (IE) had a 95% share of worldwide browser use. It was very common for Web developers to build their Websites and applications only for IE. While IE remains the market leader, the picture is now very different.

By September 2007, Internet Explorer had declined to 64% of worldwide browser use with the prospect of further decline now built into the market’s expectations (see Figure 6).

The introduction of full browsers on smartphones (think iPhone) will accelerate this cross-browser requirement. These smartphone users are one of the world’s most affluent demographics. Your Website will need to work on their device.

Cross-browser testing is now mandatory. Your AJAX testing approach will need to address this requirement.

What About Flex? I Have Pages That Use AJAX and Flex
You are an AJAX developer and really believe that it’s the best technology available for building rich Web UIs. Would you use Flex or Flash? You might not have a choice. Increasingly, marketing VPs around the world are using rich media (video, audio, flash presentations) to make product information, training, and demonstrations easily accessible to prospects and customers. Adobe Flex and Flash technology excels at the fast and efficient delivery of this content across the Web.

Until recently, the only automated testing tool for testing Flex components and applications was a special version of Mercury’s QTP (this version was only available from Adobe). In October 2007 Adobe provided access to the Adobe automation interface to testing companies, and in the next six months third-party tools will come to market incorporating the capability to test Web pages with mixed content.

What AJAX Testing Tools Are Available?
There are a number of open source and commercial offerings that support testing GUIs including browser-based UIs. Some of them are:

Open Source

  • Selenium
  • Watir, FireWatir, SafariWatir
  • Web Driver
  • PushToTest

Commercial Products

  • Mercury QTP
  • Silk
  • SWEA
  • Parasoft
  • Squish

The offerings that support AJAX testing are dominated by developer-focused, code-driven frameworks. They support AJAX testing by allowing the tester to write code that tests the browser UI. Many of the commercial offerings don’t support AJAX testing yet. The effort to write the test code can be time-consuming and expensive.

Our Choice – Selenium
Selenium (open source) offers an alternative approach. It’s implemented in JavaScript, and Selenium tests run directly in the browser just like a real user. This approach lets Selenium support many browsers on many different platforms. This is the widest cross-browser support I have seen to date.

Some important Selenium features:

  • Selenium tests are defined as simple HTML tables called “selenese” that define a simple and complete cross-browser event model. Supports Actions, Accessors, and Assertions.
  • Ability to extend Selenium. The WaitForValue and WaitForCondition extensions in Selenium are an example. These commands are important in handling timing in designing AJAX tests.

Cross-Browser, Cross-Platform Support

  • Internet Explorer 6.0 & 7.0
  • Firefox 0.8-2.0
  • Mozilla Suite 1.6+, 1.7+
  • Seamonkey 1.0
  • Opera 8 & 9

Mac OS X:

  • Safari 2.0.4+
  • Firefox 0.8-2.0
  • Camino 1.0a1
  • Mozilla Suite 1.6+, 1.7+
  • Seamonkey 1.0


  • Firefox 0.8-2.0
  • Mozilla Suite 1.6+, 1.7+
  • Konqueror
  • Opera 8 & 9

A very active support community is extending Selenium. It includes many open source contributors but also commercial software companies such as Google, TIBCO, and SOASTA.

Jason Huggins (who invented Selenium and wrote Selenium Core) now works at Google and is part of a project to implement Selenium on Google’s grid technology. See the link to the Google Test Automation Conference video featuring Jason and Jen Bevan for more details on what Google is doing. You’ll be impressed.

The TIBCO General Interface is an open source AJAX framework. Early in 2007, TIBCO released the TIBCO General Interface Test Automation Toolkit, which is a version of Selenium with extensions to support testing the AJAX components in the TIBCO General Interface.

In March of 2007, SOASTA announced its intent to provide a Web UI/AJAX/Flex testing solution as part of its strategy to provide a single integrated testing environment to support the automated testing of all Web tiers from the message layer through the browser UI. SOASTA’s implementation will subsume the “selenese” event model implemented in Selenium Core into SOASTA’s product architecture.

AJAX UI technology represents a major step forward for browser UIs but automated cross-browser testing remains challenging. Knowledge of the HTTP message stream is vital to designing successful test automation.

Available solutions require expert assembly (open source) or are developer frameworks that support writing code to test the browser UI.

Selenium delivers a different approach to solving this challenge and has gotten a lot of attention from Web developers and software vendors as a potential solution.


More Stories By Ken Gardner

Ken Gardner, executive chairman for SOASTA, is an industry veteran with more than 30 years in the enterprise software industry. He is a six-time entrepreneur having previously been the founder and CEO of Istante (acquired by Oracle in December 2004); Sagent Technology (IPO in April 1999); ReportSmith (acquired by Borland in March 1994); and ViewPoint Systems (acquired by Knowledgeware in June 1992). His first startup, in 1985, was Tesseract Corporation where he was senior vice president of Technology. From 1978 to 1985, he worked in R&D at Tymshare, Inc.

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