How to: :clap:Doing It Right Example: spies are focused on testing the requirements but as a side-effect are unavoidably touching to the internals
```javascript
it("When a valid product is about to be deleted, ensure an email is sent", async () => {
  //Assume we already added here a product
  const spy = sinon.spy(Emailer.prototype, "sendEmail");
  new ProductService().deletePrice(theProductWeJustAdded);
  //hmmm OK: we deal with internals? Yes, but as a side effect of testing the requirements (sending an email)
  expect(spy.calledOnce).to.be.true;
});
```