user.js

var requirejs = require('requirejs');
var jsdom = require('mocha-jsdom');
var assert = require('assert');

requirejs.config(require('../../config/test_config').options);

describe('models/user', function() {
    jsdom();

    // local operations on a model should be fast
    this.slow(1);

    // obnoxious setup to get mocha and require.js to play
    // well together.
    var user;
    beforeEach(function(done) {
        requirejs(['models/user'], function(_Module) {
            user = _Module;
            done();
        })
    });

    describe('instantiate', function() {
        it('should be possible to instantiate a user', function() {
            var u = new user();
            assert(typeof u !== undefined);
        });
    });
});

typeof returns a string, so line 26 should be assert(typeof u !== 'undefined');