node.js stubbing AWS S3 method in request spec with sinon - node.js

Question

I've got an express based app running on node.js 0.12.2 which uses the s3.headBucket method from aws-sdk 2.1.22 to return a JSON response depending upon whether a particular bucket exists or not.
I've been struggling to directly stub out the call to s3.headBucket with sinon. I've managed to work around this by creating an s3wrapper module which just requires the aws-sdk and instantiates and returns the s3 variable, however, I'm sure this can be done without using the wrapper module and can instead be stubbed directly with sinon, can anyone point me in the right direction?
Below is the currently working code (with the wrapper module s3wrapper.js which I'd like to remove and handle the stubbing in my status_router_spec.js file). In other words, I'd like to be able to call s3.headBucket({Bucket: 'whatever' ... instead of s3wrapper.headBucket({Bucket: ' ... and be able to stub out this s3.headBucket call with my own response.
status_router_spec.js
var chai = require('chai'),
sinon = require('sinon'),
request = require('request'),
myHelper = require('../request_helper')
var expect = chai.expect
var s3wrapper = require('../../helpers/s3wrapper')
describe('My router', function () {
describe('checking the service status', function () {
var headBucketStub
beforeEach(function () {
headBucketStub = sinon.stub(s3wrapper, 'headBucket')
})
afterEach(function () {
s3wrapper.headBucket.restore()
})
describe('when no errors are returned', function () {
it('returns healthy response', function (done) {
// pass null to represent no errors
headBucketStub.yields(null)
request.get(myHelper.appUrl('/status'), function (err, resp, body) {
if (err) { done(err) }
expect(JSON.parse(body)).to.deep.eql({
healthy: true,
message: 'success'
})
done()
})
})
})
})
})
s3wrapper.js
var AWS = require('aws-sdk')
var s3 = new AWS.S3()
module.exports = s3
status_router.js
var Router = require('express').Router
var s3wrapper = require('../helpers/s3wrapper.js')
var router = new Router()
function statusHandler (req, res) {
s3wrapper.headBucket({Bucket: 'some-bucket-id'}, function (err) {
if (err) {
return res.json({ healthy: false, message: err })
} else {
return res.json({ healthy: true, message: 'success' })
}
})
}
router.get(/^\/status\/?$/, statusHandler)
module.exports = router

Answer 1

Answering this question for the benefit of #ippomakunochi who requested a follow up response.
We ended up using rewire to directly set a stub on the s3 library. For example, we stubbed the getObject call for the s3 library using the following:
s3stub = { getObject: sinon.stub(), listObjects: sinon.stub() }
revert = s3.__set__('s3', s3stub)
Here's the complete code:
../../../build/app/helpers/s3
var AWS = require('aws-sdk');
var s3 = new AWS.S3();
module.exports = {
get: function get(options, callback) {
var requestOptions = { Bucket: module.exports.bucket(), Key: options.productId + '.json' };
s3.getObject(requestOptions, function (err, data) {
if (err) { // handle err }
try {
var productData = JSON.parse(data.Body);
} catch (e) {
// handle error
}
return callback(null, productData);
});
}
}
}
test/unit/app/helpers/s3_spec.js
var AWS = require('aws-sdk')
var chai = require('chai')
var sinon = require('sinon')
var sinonChai = require('sinon-chai')
var chaiSubset = require('chai-subset')
var rewire = require('rewire')
var s3 = rewire('../../../build/app/helpers/s3')
chai.use(chaiSubset)
chai.use(sinonChai)
var expect = chai.expect
describe('S3', function () {
var s3stub, revert
beforeEach(function () {
s3stub = { getObject: sinon.stub(), listObjects: sinon.stub() }
revert = s3.__set__('s3', s3stub)
})
afterEach(function () {
revert()
})
describe('#get', function () {
context('when no errors are returned by s3', function () {
it('returns a product', function (done) {
var productResponse = helper.fixture.body('product.json')
s3stub.getObject.yields(null, productResponse)
s3.get({ productId: '1234' }, function (err, res) {
expect(err).to.not.exist
expect(res).to.containSubset({name: 'long sleeve shirt', 'retailer_code': 'retailer-1'})
done()
})
})
})
context('when s3 returns a NoSuchKey error', function () {
it('returns a NotFoundError', function (done) {
var s3Error = AWS.util.error(new Error(), { name: 'NoSuchKey' })
s3stub.getObject.yields(s3Error)
s3.get({ productId: '1234' }, function (err) {
expect(err.message).to.eql('1234 is not found in s3')
expect(err.output.statusCode).to.eql(404)
done()
})
})
})
})