Stubbing S3 uploads in Node.js

Question

How would I go about stubbing S3 uploads in Node.js?

For insight, I'm using Mocha for tests and Sinon for stubbing, but I'm open to changing anything. I have a file that exports a function that performs the upload. It looks like this:

var AWS = require('aws-sdk');
var s3 = new AWS.S3({ params: { Bucket: process.env.S3_BUCKET }});
var params = { Key: key, Body: body };
s3.upload(params, function (error, data) {
  // Handle upload or error
});

If I try to stub AWS.S3 or AWS.S3.prototype, nothing changes. I assume this is because my tests have required aws-sdk themselves and have their own copy of each function.

My test looks like this:

describe('POST /files', function () {
  var url = baseURL + '/files';
  it('uploads the file to s3', function (done) {
    var fs = require('fs');
    var formData = {
      video: fs.createReadStream(process.cwd() + '/test/support/video.mp4')
    };
    var params = {url: url, formData: formData};
    request.post(params, function (error, response, body) {
      expect(response.statusCode).to.eq(200);
      expect(response.body).to.eq('Uploaded');
      done();
    });
  });
});

This test works fine, but it does not stub the upload to S3, so the upload actually goes through :X.

Answer 1

There are several options to mock S3 in Node.

Some modules specific to S3:

• https://www.npmjs.com/package/mock-s3
• https://www.npmjs.com/package/mock-aws-s3

Some modules for general AWS mocking:

• https://www.npmjs.com/package/aws-sdk-mock
• https://www.npmjs.com/package/mock-aws-sinon
• https://www.npmjs.com/package/mock-aws

And you can even start a simple server that responds to some of the S3 API calls:

• https://www.npmjs.com/package/s3rver

The last one can easily be used in other languages and runtimes, not only in Node.

Answer 2

You can stub with Sinon.js as follows if you'd like:

1. Expose the AWS.S3 instance:

   var AWS = require('aws-sdk');
   var s3 = new AWS.S3({ params: { Bucket: process.env.S3_BUCKET }});
   var params = { Key: key, Body: body };
   exports.s3.upload(params, function (error, data) {
   
   });
   //Expose S3 instance
   exports.s3 = s3;
   

2. Stub the same instance like so:

   var sinon = require('sinon');
   //Import module you are going to test
   var UploadService = require('./uploadService');
   
   describe('POST /files', function () {
   
     before(function() {
       //Stub before, and specify what data you'd like in the callback.
       this.uploadS3Stub = sinon.stub(uploadService.s3, 'upload').callsArgWith(1, null, { data: 'Desired response' });
     });
   
     after(function() {
       //Restore after
       this.uploadS3Stub.restore();
     });
   
     var url = baseURL + '/files';
     it('uploads the file to s3', function (done) {
       var fs = require('fs');
       var formData = {
         video: fs.createReadStream(process.cwd() + '/test/support/video.mp4')
       };
       var params = {url: url, formData: formData};
       var self = this;
   
       request.post(params, function (error, response, body) {
         expect(response.statusCode).to.eq(200);
         expect(response.body).to.eq('Uploaded');
         //You can also check whether the stub was called :)
         expect(self.uploadS3Stub.calledOnce).to.eql(true);
         done();
       });
     });
   });