Lessons Learned: Migrating from Selenium 1 to Selenium 2

Posted Jul 21st, 2011

This guest blog post was written by Roger Hu, Software Engineer at Hearsay Social. At Hearsay Social, we've upgraded our testing environment to use Selenium 2. We made the switch because there was enough evidence to suggest a huge 2-4x performance increase. Having learned a few lessons along the way, we thought it would be helpful to share what we found, especially for those who are considering making the transition.
  • Since Selenium 2 is redesigned to leverage what works best for the browser, whether it's a NPAPI plugin in Firefox or a DLL module for IE, we've discovered a huge performance gain, especially in Internet Explorer (IE) browsers that have much slower JavaScript engines. The new approach seems to allow us to run Selenium more conveniently on Internet Explorer browsers without the hassle of changing the security options because of all the exceptions that were thrown as a result of the older JavaScript-based architecture.
  • Selenium 2 gets closer to simulating the behavior of a user on a browser.  In Selenium 2, the DOM element that is actually clicked is determined by the X/Y coordinates of the mouse event. Therefore, if you attempt to search for a DOM element that is hidden or obstructed by another element, the top element will always be fired and you might encounter ElementNotVisibleException errors from the Selenium server. You need to keep this issue in mind when rewriting your tests, since Selenium 1 versions may not have had this restriction. (We use the Django web framework and the popular django-debug-toolbar, which adds a popup overlay in our web application that has to be disabled in our application during Selenium tests.)
  • We've found that the new Selenium 2 WebDriver-based API is easier to train our developers to use. The documentation for Selenium 2 is still somewhat sparse, especially for the updated Python bindings, so digging into the source code (in our case, remote/webdriver.py and remote/webelement.py code) is still the best way to learn what API commands are available. While Java developers may have access to WebDriverBackedSeleniumclass that can use existing Selenium 1 code while leveraging the WebDriver-based API, we didn't find any similar support for Python. So we took the plunge and refactored most of our tests. webdriver/remote/webelement.py:
        def tag_name(self):
            """Gets this element's tagName property."""
            return self._execute(Command.GET_ELEMENT_TAG_NAME)['value']
        def text(self):
            """Gets the text of the element."""
            return self._execute(Command.GET_ELEMENT_TEXT)['value']
        def click(self):
            """Clicks the element."""
        def submit(self):
            """Submits a form."""
        def clear(self):
            """Clears the text if it's a text entry element."""
On the server-end, it's important to study how the client API is sending remote commands by reviewing the JsonWireProtocol document posted on the Selenium Wiki, especially since Sauce Labs provides you with the raw logs to see what commands are actually being issued by the client.
  • While experimenting with Selenium 2, we found it much easier to test out the new WebDriver API by downloading and running the Selenium server locally. This way, your connection won't constantly timeout as a result of using your Sauce Labs account, giving you more freedom to experiment with all the various commands. If you need to run browser tests against an external site while using your own machine to drive the browser interactions, you can setup a reverse SSH tunnel and then experiment with Selenium 2 API by setting debugger breakpoints and testing out the API bindings. In the long-term, though, you definitely want to use Sauce Labs for hosting all the virtual machines in the cloud for running your browser tests!
  • If you're interested in using Firebug to help debug your application, Selenium 2 also provides a way to inject Firefox profiles. You can create a Firefox profile with this plug-in extension, and Selenium 2 includes an API that will base-64, zip-encode the profile that will be downloaded by the remote host. Note that this approach works best if you're running the Selenium server locally, since using it over a Sauce Labs instance only gives you access to view the video.
  • Selenium 2 continues to be a moving target with its API, so you'll want to keep up to date with any release notes posted on the Selenium HQ blog. Most recently, we found that the toggle() and select() commands have not only been deprecated but removed completely from the implementation. If you try to issue these commands, the Selenium server simply doesn't recognize the commands and WebDriverExceptions are raised. The best thing to do is look at the Selenium version number. In this particular example, version 2.0.0 (three decimal places) are used to represent the release candidate of the latest Selenium build. You may also instantiate your .jar files with the -debug flag to watch how your client bindings execute API commands to the Selenium server.
20:38:02.687 INFO - Java: Sun Microsystems Inc. 20.1-b02
20:38:02.687 INFO - OS: Windows XP 5.1 x86
20:38:02.703 INFO - v2.0.0, with Core v2.0.0. Built from revision 12817
  • Selenium 1 users will find that is_text_present() and wait_for_condition() commands no longer exist, and are replaced by a more DOM-driven approach of selecting the element first before firing click() events or retrieving attribute values through get_attribute(). You no longer have to have wait_for_condition() for page loads. Instead, you set implicitly_wait() to a certain timeout limit to rely on find_element_by_id() to wait for the presence of DOM elements to appear to between page loads.
  • Lastly, we've noticed in the Selenium discussion groups that often there are questions about how to deal with concurrent Ajax requests during your tests.  In many test frameworks, there's the concept of setup and tear down of the database between each set of tests.  One issue that we encountered is that if your browser is issuing multiple requests, you're better off waiting for the Ajax requests to complete in your tear down function since the requests could arrive when the database is an unknown state. If this happens, then your Selenium tests will fail and you're going to spend extra time trying to track down these race conditions. If you're using jQuery, you can check the ajax.global state to determine whether to proceed between pages (i.e. execute_script("return jQuery.active === 0")). You'll want to keep looping until this condition is satisfied (for an example of implementing your own wait_for_condition() command, click here.)
Hope you find these tips helpful for migrating over to Selenium 2. Happy testing!

Written by

Roger Hu


SeleniumCross-browser testing