Stub/spy on singleton with Sinon

Question

I have a need to write some unit tests where I check on calls to singleton functions. Basically, if I have this:

const somePackage = require('some-package');

And am calling it with:

somePackage();

I want to be able to spy/stub on this singleton call to prove that it was called. I know how to do this with methods using sinon.stub(somePackage, 'someMethod') but not for just a singleton.

Right now I actually have to write integration tests by executing the code when in reality I want to write unit tests and show that these external methods were called. I'm trusting that the developer of those packages did their own testing for the functionality.

Answer 1

You can spy on any function with sinon:

const spy = sinon.spy(myFunc);

To stub a single function you can use proxyquire as described in this issue :

const proxyquire = require('proxyquire')
const sinon = require('sinon')
const sum = sinon.stub()

const ModuleWithDependency = proxyquire('module', {
  'sum': sum
})