REST API testing using vows, tobi and node.js

I am trying to combine the examples here, here to write a vows test for my node.js / express app that:

1. Creates a new user object
2. Checks the response was sane
3. Uses the returned _id to test looking up the newly created user
4. Again uses the _id to test updating the user

Item 1 and 2 work fine, but there is something wrong with my sub-context 'GET /users/:id'. It errors and I cannot figure out why. Tried Googling and using the debugger, but I still can't see what it is, I am probably just overlooking something obvious.

···✗ Errored » 3 honored ∙ 1 errored

Can anyone tell me why the 4th vow errors?

Here's my vows code:

var vows = require('vows')
  , assert = require('assert')
  , tobi = require('tobi')

var suite = vows.describe('Users API')
  , now = new Date().getTime()
  , newUser = { name: now + '_test_user', email: now + '@test.com' }
  , browser = tobi.createBrowser(3000, 'localhost')
  , defaultHeaders = { 'Content-Type': 'applica开发者_如何学Gotion/json' }

function assertStatus(code) {
  return function (res, $) {
    res.should.have.status(code)
  }
}

var client = {
  get: function(path) {
    return function() {
      browser.get(path, { headers: defaultHeaders }, this.callback)
    }
  },
  post: function(path, data) {
    return function() {
      browser.post(path, { body: JSON.stringify(data), headers: defaultHeaders }, this.callback)
    }
  }
}

suite.addBatch({
  'GET /users': {
    topic: client.get('/users'),
    'should respond with a 200 ok': assertStatus(200)
  },
  'POST /users': {
    topic: client.post('/users', newUser),
    'should respond with a 200 ok': assertStatus(200),
    'should return the new user': function(res, $){
      assert.isNotNull(res.body._id)
      assert.isNotNull(res.body.created_at)
      assert.isTrue(res.body._id.length > 0)
      assert.equal(newUser.name, res.body.name)
      assert.equal(newUser.email, res.body.email)
    },
    'GET /users/:id': {  // Sub-context of POST /users
      topic: function(res) { return client.get('/users/' + res.body._id) },
      'should respond with a 200 ok': assertStatus(200)
    }
  }
})

suite.export(module)

EDIT

I tried simplifying the code as follows to help see if this.callback was the problem, but the error is still there:

'GET /users/:id': {  // Sub-context of POST /users
  topic: function(res) {
    console.log('About to request /users/' + res.body._id)
    browser.get('/users/' + res.body._id, { headers: defaultHeaders }, this.callback)
  },
  'should respond with a 200 ok': assertStatus(200)
}

How are you populating res for the fourth tes?? It wouldn't be visible outside the line

'should return the new user'

Try creating the id variable outside the addBatch call, and set it in the third test. then call

client.get('/users/' + id)

EDIT:

Better yet, put it back into newUser in the third test:

'should return the new user': function(res, $){
  newUser.id = res.body._id
....

and then do:

client.get('/users/' + newUser.id)