Example of mocha testing for https://github.com/justin-john/node-user-management/blob/master/routes/users.js#L107-L146, you can add more testing in error conditions

gistfile1.js

var should = require('chai').should();
var superagent = require('superagent');

var agent;

describe('testing user', function(){
  
    before(function (done) {
  	  agent = superagent.agent();
      // some other operation you need
      // like drop your collection for testing o adding something
  	});  
    
    it('should not register a user with a weak password', function (done){
    agent
  		.post(route.signup)
  		.send({username: 'This is a valid name'})
  		.send({email : 'my@example.com'})
  		.send({pwd : ''})
  		.end(function (req, res) {
  			res.should.have.property('text').that.contain('The password can\'t be empty and 6 - 16 characters required');
  			done();
  		});
  });
  
  it('registers a new user', function (done) {
  	agent
  		.post(route.signup)
  		.send({username: 'My_name'})
  		.send({email : 'my@example.com'})
  		.send({pwd : '123456a'})
  		.end(function (req, res) {
        res.should.have.property('statusCode').that.equals(200);
  			res.should.have.property('text').that.contain(username);
  			done();
  		});
  });
  
  it('fails to register a new user with a registered email', function (done) {
  	agent
  		.post(route.signup)
    	.send({username: 'My_name'})
  		.send({email : 'my@example.com'})
  		.send({pwd : '123456a'})
  		.end(function (req, res) {
  			res.should.have.property('statusCode').that.equals(200);
  			res.should.have.property('text').that.contain('This email is already taken!');
  			done();
  		});
  });
  
  
});