How to mock AWS S3 getObject with sinon

Question

I'm trying to unit test a restify route that returns an S3 object from a bucket

my route is:

 module.exports = function(server) { server.get('/configs/:version', (req, res, next) => { const s3 = new AWS.S3(); const params = { Bucket: 'testBucket', Key: 'testKey' }; function send(data, next) { res.setHeader('Content-Type', 'text/plain'); res.setHeader('Cache-Control', 'no-cache'); res.status(200); res.send(data.Body); next(); } s3.getObject(params, (err, data) => (err) ? next(err) : send(data, next)); }); };

For my unit test I've been trying to mock the S3 constructor so I can stub getObject and failing miserably.

 describe('#configs', () => { let req; let res; let next; let server; let config; let AWS; let S3; let route; beforeEach(() => { req = { params: { version: 'testVersion' } }; res = { send: sinon.spy(), }; next = sinon.spy(); server = { get: sinon.stub(), }; config = { get: sinon.stub(), } AWS = () => { return { S3: () => { return { getObject: sinon.stub() } } } } route = proxyquire(process.cwd() + '/lib/routes/configs/get', { 'configs.js': config, 'aws-sdk': AWS, }); route(server); }); describe('#GET', () => { it('Should register configs get route', () => { let s3 = sinon.createStubInstance(AWS.S3, { getObject: sinon.stub(), }); server.get.callArgWith(1, req, res, next); expect(server.get).calledOnce.calledWith('/configs/:version'); expect(s3.getObject).calledOnce.calledWith({ Bucket: 'testBucket', Key: 'testKey' }); }); }); });

But I getting this error: TypeError: undefined is not a spy or a call to a spy! on the getObject method. After reading sinon docs over and over again I can't understand how to mock the constructor, how can I stub the getObject method so I can make sure it's being called correctly and it's returns so I know it's responses are being treated correctly Can someone help me with this?

Answer 1

Finally made my mocks work, the issue was that I was mocking AWS as a function not has an object, it's S3 that needs to be mocked as a function, because it's S3 that needs to be instantiated. This is how the mock should look like:

function S3() { 
  return s3;
}

s3 = {
  getObject: sinon.stub(),
  putObject: sinon.stub()
};

AWS = {
  config: {
    update: sinon.stub()
  },
  S3: S3
};

Like this if one needs to mock putObject, he just needs for example do this: s3.putObject.callsArgWith(1, err, data);

Answer 2

const getObjectStub = AWS.S3.prototype.getObject = Sinon.stub();
    getObjectStub.yields(null, {
    AcceptRanges: "bytes", 
    ContentLength: 3191, 
    ContentType: "image/jpeg", 
    Metadata: {
    }, 
    TagCount: 2, 
    VersionId: "null"
   }
);