ActionScript 3 :: Testing And Mocking With Flex

I am developing a "dumb" front-end, it's an AIR application that interacts with a "smart" LiveCycle server. There are currently about 20 request & response pairs for the application. For many reasons (testing, developing outside the corporate network, etc), we have several XML files of fake data, and if a certain configuration flag is set, the files are loaded, a specific file is parsed and used to create a mock response. Each XML file is a set of responses for different situation, all internally consistent. We currently have about 10 XML files, each corresponding to different situation we can run into.

This is probably going to grow to 30-50 XML files. The current system was developed by me during one of those 90-hour-week release cycles, when we were under duress because LiveCycle was down again and we had a deadline to meet. Most of the minor crap has been cleaned up. The fake data is in an object called FakeData, with properties like customerType1:XML, customerType2:XML, overdueCustomer1:XML, etc. Then in the FakeData constructor, all of the properties are set like this:

customerType1:XML = FileUtil.loadXML(File.applicationDirectory.resolvePath("fakeData/customerType1.xml");

And whenever you need some fake data (this happens in special FakeDelegates that extend the real LiveCycle Delegates), you get it from an instance of FakeData. This is awful, for many reasons, but it works. One embarrassing part is that every time you create an instance of FakeData, it reloads all the XML files. If there's a design pattern that is not Singleton that can handle this more elegantly. The constraints are:

No global instances can be required (currently, all the code dealing with the fake data, including the fake delegates, is pulled out of production builds without any side-effects, and it needs to stay that way). This puts the Factory pattern out of the running. It can handle multiple objects using the XML data without performance issues. The XML files are read centrally so that the other code doesn't have to know where the XML files are, and so some preprocessing can be done (like creating a map of certain tag values and the associated XML file).