The short question: How do you follow Test-Driven Development on a project that spans multiple languages?

Specifically, I'm writing a web application that uses JavaScript and PHP, and I want to follow the TDD principles, but I'm not sure how to integrate them. Do I run separate test suites for the JS and PHP sections, and use mocks in the JS suite to emulate server responses? Is there a technique or framework for unit testing both components in one run?

This is my first experience using Test-Driven Development, so any advice you can share on how to make it less daunting would be great. The reason I chose it is that as soon as I finished a prototype, the requirements changed, forcing me to change my design. I figured if I'm starting over, I'd like to write more extensible code with built-in regression testing from the start.