Flexunit Asyncrhonous Setups

If you ever need to load some external data before running a test, or need to wait for a component's creation complete event, then you know the inadequacies of the Flexunit framework when it comes to asynchronous operations. One approach you might think of is to load the XML data, for example, in the setUp() method and attach a handler to the loader to wait for the complete event which would then call runMiddle() so the actual test body runs. You would need to override the runMiddle() method in your test case, and call super.runMiddle() in your complete handler. However, while this will cause the tests to run properly after the data has become available, Flexunit will not hang around long enough to catch the passed/failed asserts in your test body. You will instead get a runtime error box telling you which asserts failed, and a green bar from the Flexunit UI. This is not desirable. What we need then is to somehow write a test case that begins loading the data, and somehow specifies which method to run that contains the actual asserts for the test method. Essentially if you wanted to do really simply you would just load the data with a Loader object, attach a complete handler to the loader wrapped with the addAsync method of the TestCase to delay test execution, and write the complete handler so that it accepts the complete event and does what it will with the event.currentTarget. I would rather have a general asynchronous setup method that takes as parameters the URL of the data to load, the test handler with all the asserts, and the class of the data that should be loaded. Instead of a jumble of words explaining this it would probably help more to just paste the code at this point.

package {
    import flash.events.Event;
    import flash.net.URLLoader;
    import flash.net.URLRequest;

    import flexunit.framework.TestCase;

    public class AsyncSetupTestCase extends TestCase {

        public var data:*;
        public var returnType:Class;

        public function setupAsync(target:String, test:Function, returnType:Class):void {
            this.returnType = returnType;
            var helper:Function = this.addAsync(this.completeHandler, 1000, test);
            var loader:URLLoader = new URLLoader();
            loader.addEventListener(Event.COMPLETE, helper);
            loader.load(new URLRequest(target));

        private function completeHandler(event:Event, test:Function):void {
            trace('async load complete');
            this.data = event.currentTarget.data as this.returnType;


As the previous code demonstrates, I have simply extended Flexunit's TestCase class and added a few methods to help with asynchronous setups. Essentially all a test case that needs to load external data must do then is to call the setupAsync method with the desired information, and AsyncSetupTestCase will handle running the test once the load is complete. All the designated handler in the test needs to do differently from other tests is to a) not be prefixed with test and b) use the data property to access the loaded data from the setup. An example test case demonstrating this follows:

public function testMethod():void {
    this.setupAsync('something.xml', this.doTestMethod, XML);
public function doTestMethod():void {
    // do what we will with this.data, it shall be an XML instance
    assertTrue(this.data is XML);
Ben Snider

Benjamin Snider

Hi! 👋 I'm Ben and I like to write about technical and nerdy things. Historically about Swift and iOS. But, I've recently started a masters program in computer science (Georgia Tech's OMSCS), so the content here may pivot as such.  Get @me!