testing node express endpoint and stub 3rd party api call

I have an express app like this:

server.js

const postsController = require('./controllers/posts_controller.js')
module.exports = app = express()
app.get('posts', postsController.index)

posts_controller.js

const thirdPartyApi = require('third_party_api')

module.exports = {
  index: (req, res) => {
    thirdPartyApi.get().then((posts) => {
      res.status(200).send(posts)
    }, (error) => {
      res.status(400).send('text')
    })
  }
}

spec/posts_controller_spec.js

const app = require('../server')
const request = require('supertest')

describe('GET /posts', () => {
  it('should retu a collection of posts', () => {
    request(app)
     .get('/posts')
     .end((_err, resp) => {
       expect(resp.status).toEqual(200)
     })
  })
})

My goal here is to stub out the thirdPartyApi.get(). I tried with proxyquire by adding this line to posts_controller_spec:

proxyquire('../posts_controller', {third_party_api: {
  get: () => { console.log('stubbed out get method'); }
})

This doesn't work because the server.js file is the file that requires the third_party_api again.

I could do something like this to test the controller:

const postsController = proxyquire('../posts_controller', {third_party_api: {
  get: () => { console.log('stubbed out get method'); }
})


postsController.index(req, res)

This second strategy doesn't feel right because now I have to stub req and res and now I'm bypassing the actual app instance.

Is there an easy way to do this, with proxyquire, or otherwise?