Sinon stub on prototype, check value of actual instance it is called on

Question

I have a sinon stub on a prototype and method...

stub = sinon.stub(MyType.prototype, 'someFunction');

MyType has some value in a property depending on which instance it is. Lets call the property identifier.

I need to check two things...

1. That someFunction was called with the correct parameters. expect(stub).to.have.been.calledWith('Some Parameter'); (This works as expected).

2. That the identifier of the instance the function was called on is correct. There are many instances of MyType and I need to check the function was called on the correct one.

I can do the first check. But I don't know how to (or even if) I can do the second check.

Is this possible?

Thanks

Answer 1

Yes, this is possible.

You can use sinon.assert.calledOn, spy.calledOn, spyCall.thisValue, or spy.thisValues to check the this value for calls:

import * as sinon from 'sinon';

class MyType {
  constructor(id) {
    this.identifier = id;
  }
  someFunction(arg) { }
}

test('someFunction', () => {
  const stub = sinon.stub(MyType.prototype, 'someFunction');

  const one = new MyType("oneId");
  const two = new MyType("twoId");

  one.someFunction('firstArg');
  two.someFunction('secondArg');

  sinon.assert.calledWith(stub.firstCall, 'firstArg');  // SUCCESS
  sinon.assert.calledOn(stub.firstCall, one);  // SUCCESS
  expect(stub.firstCall.thisValue.identifier).to.equal('oneId');  // SUCCESS

  sinon.assert.calledWith(stub.secondCall, 'secondArg');  // SUCCESS
  sinon.assert.calledOn(stub.secondCall, two);  // SUCCESS
  expect(stub.secondCall.thisValue.identifier).to.equal('twoId');  // SUCCESS
});