Stubbing S3 uploads in Node.js - 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:
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;
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();
});
});
});

Answer 3

s3UploadStub = AWS.S3.prototype.upload = sandbox.stub();
it("should upload successfully", async function() {
s3UploadStub.yields(null, data);
let response = await FileUtil.uploadFile(fileReference,data);
expect(s3UploadStub.calledOnce).to.be.true;
expect(response.statusCode).to.equal(200);
expect(response.body).to.equal(fileReference);
});

Answer 4

You need to create stubs using sinon and replace the variables in the code you're testing with the stubs. There are a few modules to do this, try Mockery or Rewire. For example with Rewire you load the module you're testing using rewire instead of require then use __set__ to set the variables.
var rewire = require('rewire');
var moduleUnderTest = rewire('myModule');
moduleUnderTest.__set__('s3', stubbedS3);