To hack on Faye, you'll need Node in order to build both the gem and the npm package. The following should get you up and running:
# Download the code from Git
git clone git://github.com/faye/faye.git
cd faye
# Install dependencies
bundle install
npm install
# Build Faye
npm run-script build
# Run tests
bundle exec rspec -c spec/
node spec/node.js