How to ignore modules from the karma config file with browserify

I'm trying to test React.js with testdom, which requires jsdom. I'm using karma with browserify. jsdom cannot be browserified, so I'd like to ignore it.

The problem I have is trying to do this from within the karma.config.js file.

browserify: { debug: true, transform: [ "babelify" ], ignore: [] or {} or...??? },

Help!