If you clone the jstest-driver project code you will be able to see how it works.
    git clone https://code.google.com/p/js-test-driver/

*To explain this you will need to see this two files:*

**Path file:**
JsTestDriver\JsTestDriver\src\com\google\jstestdriver\javascript\TestCaseBuilder.js

**Line Number: 115**

In this file you can see the declaration of ConditionalTestCase

**Path file:* *
JsTestDriver\JsTestDriver\src\com\google\jstestdriver\javascript\config.js

**Line Number: 46 & 47**

In this other file you can see how ConditionalTestCase is declared as global.