Should-Node is a project mainly written in JavaScript, it's free.
An assertion library for Node.js
An assertion library for Node.js. Allows for very intuitive assertion testing. It embraces and encourages Behavior Driven Development.
Example: someObject.should.be.an.instanceof(Objet); or aString.should.be.a.string
Documentations: http://mansoorsayed.com/should-node/docs/