Asynchronous events and Mochitesting

Recently, I found that I needed my chrome Mochitest to wait for a XBL binding to apply, before continuing the test. For the end-user, waiting is hardly an issue – by the time they see the new user interface, all the bindings have applied. Mochitest (and most other automated test harnesses) runs straight through, and brakes for nobody. In some cases you can pull some trickery with nsIThreadManager, convincing Firefox to wait… but that’s hardly reliable.

So I came up with a three-part solution.

  1. Force my XBL bindings to fire DOM events when the constructor executes.
  2. Break up my test functions into (slightly) smaller functions, each of which handles a part of the overall test. Two parts cover the main functional testing, while a third part is specific to the XBL binding.
  3. Implement a generic testing harness for Mochitest which can manage the flow from one function to another.

This new test harness, which I call PendingEventsTest, adds a layer of complexity on top of SimpleTest. Each test function is added via PendingEventsTest.addTest(), and you can pause for a DOM event with PendingEventsTest.addEventLock(). The whole test sequence can abort with an error by calling PendingEventsTest.abortFail(). You can advance to the next test function in the sequence with PendingEventsTest.asyncRun() or

There’s more complexity to it than that, of course. To move data from one test function to another, I also added “payload” support, for storing a generic object. Also, this is written for chrome Mochitests – it will likely fail in content Mochitests. Still, this new test harness helped me finish support in Verbosio for my equivalent of the <xbl:children/> element in markup templates.

Lastly, it (and the logging service I wrote a few weeks ago) is licensed under MPL 1.1/GPL 2.0/LGPL 2.1, so anyone who wants to borrow this for Mozilla code is welcome to. Cheers!

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