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Selenium test for computedStyle

June 28 2011 : posted under css testing selenium

I wanted to write some automated tests for CSS changes and bugs, these type of issues are quite prone to regression so re-running the tests has a large benefit.

It is possible to add new assertions to selenium via the user-extensions.js file

The following adds a test for computed style, this only works in firefox as far as I know - but some automation is better than none

//only works in firefox
Selenium.prototype.assertStyle = function (locator, text) {
  var params = text.split("=", 2);

  var propertyName = params[0];
  var expectedValue = params[1];

  var element =;
  var actualValue = this.browserbot
    .getComputedStyle(element, null)
  Assert.matches(expectedValue, actualValue);

Now I can add a selenium test like


Selenium only lets me pass two parameters and really I want three (locator, css property, expected value). So I’ve hacked this and put two parameters into one - which is a bit smelly but for now gets the job done - comments on better methods very welcome.

I need to at least check that the ‘text’ parameter is validated properly - but I figured I’d blog now and update later as I’ve a deadline to meet today.