Get instance of running server | Node.js

I'm making unit-test for my server application. I need to test REST API. I'm using supertest and mocha to create these tests.

I running server like this in the hooks(local server test)

server = require("#{__dirname}/../../core/start")
    .then () ->
      done()
    .catch (error) ->
      done error

in ../../core/start.js

module.exports = new Promise (resolve, reject) ->
  server.listen (config.get 'port'), (config.get 'ip'), (err) ->
    if err then return log.error err: err
    app.emit 'open',
      port: config.get 'port'
      ip: (config.get 'ip')

  Promise.all([
    new Promise (resolve, reject) ->
      app.once 'open', () ->
        resolve null
    new Promise (resolve, reject) ->
      mongoose.connection.once 'open', () ->
        resolve null
  ]).then () ->
    resolve IoC

Can I handle variables in this promise ? I need to mockup some functions, because they communicate with other server(I need to mockup this).