Getting Started with Selenium

Selenium is a neat little tool for integration testing with browser automation. If you’re not familiar with it already, check it out. The Selenium IDE can record and playback actions on your browser, with the caveat that it’s normal to have to go back and manually tweak some of the steps that it recorded. Here are some notes from when I first started out with it, and some issues that I worked through. Hopefully reading this will save you some headaches.

The native file format for tests cases in Selenium IDE is html, but you can convert Selenium IDE files into unit tests in the language of your choice. The big advantage of this is running automated tests as a part of your build process. For Java, navigate to file -> export test case as -> java / junit 4 / webdriver. Selenium unit tests need to run on a machine that has graphics capabilities so it can open a browser, but it is possible to configure a headless machine to run selenium. Some gotchas related to unit testing with selenium test cases:

  • Tests tend to be brittle. If you start building a complete test suite with code, look into the Page Object pattern, this will make your test more resilient.
  • If a unit test fails an assertion, the rest of the test will fail to run, which can hurt if each test does setup and teardown for itself and subsequent tests expect a “clean” state before they start running. It’s best to not depend on teardown steps in your test.
  • If you’re testing with webdriver and firefox, then firefox must be shutdown before running selenium tests because selenium currently can’t attach to a running instance and a new instance of firefox can’t be started if it’s already running.
  • Selenium must run in sequence per machine, they can’t be run in parallel tests because of the aforementioned firefox issue. Parallelized selenium tests can be achieved with selenium grid.

One thing that you generally have to tweak in any tests generated by Selenium IDE is the timing of the steps. When you record, you have natural pauses in your activity but the test case runs each step one after the other as quickly as possible. I had a test case that hit an update button, verified the response, and logged out at the end of the case. However the javascript that would have received the update response stopped running on logout, and verification subsequently failed. You need careful use of andWait / waitFor / pause commands to make sure your app functions correctly under test. Also, if you use a pause or a clickAndWait as the last command of a case (say, to log out at the end of a test case), the case will not actually pause or wait because the time is added to the beginning of the next step of a test case, not the end of the current command. You can get around this by putting an echo as the last command of the case.

Sometimes the selectors that Selenium IDE generates are either too brittle or not working at all. One thing to try is to select the element you want to click in firebug and view the xpath from that, and use that in the selenium step. Another (preferred) option is to be more intelligent about how you select it, say by selecting element by text content or by css class if you know that they will be unique on the page.


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