When it's up and running, our application still has one giant dependency: the server. During integration testing, this means that the server-side database needs to be primed with test data, and test suite will result in many requests being sent back and forth. In a large test suite, this can be slow and the database setup can be painful.

A common resolution to this problem is to bypass the server API altogether. When our application makes an Ajax request, we can hijack the XMLHttpRequest and feed the calling code some static test data instead.

To demonstrate this and show the flexibility of the technique, we'll create a small Jasmine test case that shows how to supply a product store with mock JSON data. Although, faking an Ajax request is really useful in integration tests, this will show off the technique in a succinct way that can be used in both unit and integration testing.

We'll be using a feature of Ext JS that isn't included by default: Simlets. The classes that...