node.js - stubbing a Mongoose model -

i'm trying unit test function:

exports.createtoken = function( user ){    var tokenexpirationdate = moment().add( config.tokenexpiration, 'minutes' ).valueof(),       payload = {         sub: user.id,         exp: tokenexpirationdate       },       token = jwt.sign( payload, config.tokensecret ),       userinfo = user.tojson();    delete userinfo._id;   delete userinfo.__v;   delete userinfo.password;    return {     user: userinfo,     token: token,     expires: tokenexpirationdate   }; }; 

since idea not have dependencies, have stub mongoose model function receives.

since have little no experience in unit testing first thought in mocha:

describe( '#createtoken', function() {   it( 'should return jwt token', function( done ) {      var fakeusermodel = {        id: '558480eeffa8528c15492361',        _id: '558480eeffa8528c15492361',        __v: '0',        tojson: function(){          return {            email: 'foo@bar.org',            password: '123456',            username: 'foo'          }        }      }      var token = auth.createtoken(fakeusermodel);      token.should.have.property('user').and.be.an( 'object' );     token.user.should.have.property('email','foo@bar.org').and.be.a('string');     token.user.should.have.property('username','foo').and.be.a('string');     token.should.have.property('token').and.be.a( 'string' );     token.should.have.property('expires').and.be.a( 'string' );      done();   }); }); 

is there way achieve this, perhaps using sinon/rewire ?