I'm working on UI testing an ExtJS web-app, and I'm a beginner. 
I am trying to test the ExtJS widgets by using CasperJS/PhantomJS tool.
Also, I generate the required CasperJs script using [Resurrectio](https://github.com/ebrehault/resurrectio) and by making necessary changes to it.

Since ExtJs generates unique ids dynamically for the DOM elements that it creates, I want to know how to provide those ids in CasperJs script for testing.

For example, The following Casper Script was generated by Resurrectio:

```
   casper.waitForSelector("#ext-gen1142 .x-tree-icon.x-tree-icon-parent",
       function success() {
           test.assertExists("#ext-gen1142 .x-tree-icon.x-tree-icon-parent");
           this.click("#ext-gen1142 .x-tree-icon.x-tree-icon-parent");
       },
       function fail() {
           test.assertExists("#ext-gen1142 .x-tree-icon.x-tree-icon-parent");
   });
   casper.waitForSelector("#gridview-1038",
       function success() {
           test.assertExists("#gridview-1038");
           this.click("#gridview-1038");
       },
       function fail() {
           test.assertExists("#gridview-1038");
   });

```

Here #ext-gen1142 and #gridview-1038 are the ids dynamically created. How should one provide data in the tests? Is there any stub or mocking tools which works with ExtJs in the code to provide these ids at runtime during tests?

I came across [SinonJS](http://sinonjs.org/). Can it be used or Do I need to used CSS or XPath Locators as mentioned in this [answer](https://stackoverflow.com/questions/107314/any-suggestions-for-testing-extjs-code-in-a-browser-preferably-with-selenium)? How reliable it is to use CSS or Xpath Locators?

Thanks in advance!