Stubbing library constructor calls with sinon

Question

Up until now I have been using sinon to stub out function calls on objects included in my nodeJS code.

For example I use the request library, and so in my tests I can stub out http calls like:

var request = require('request');
//Somewhere further below in my tests:
postStub = sinon.stub(request, 'post');

I have now hit a scenario where a library I am including needs to be called like so in my actual code:

var archiver = require('archiver');
//Further below in actual code (express middleware)
var zip = archiver('zip');
zip.pipe(res);

I want to be able to stub out calls to pipe() on the archiver library, but I think I need to stub out the constructor call first - archiver('zip') ?

I have had a search around and I think sinon's createStubInstance could help me here, but I am not 100% sure.

Can someone assist? Thanks

Answer 1

It's not pretty but what i've done seems to work. Wrap your un-stubbable library function with another exportable method.

file.js

exports.originalMethod = function() {
  var archiver = require('archiver');
  //Further below in actual code (express middleware)
  var zip = exports.newArchiverMethod('zip');
  zip.pipe(res);
}
exports.newArchiverMethod = function(arg) {
  return archiver(arg);
}

This newArchiverMethod can then be stubbed.

spec.js

archiverStub = sinon.stub(controller, 'newArchiverMethod');

It's not perfect because it adds a new exportable method and it creates unnecessary clutter in the original file, as well as a non-testable line. But it does let you get past this one line and test the rest of a long method.