Chai: assert error objects

[ghost]

I have a function that is passing an error object to it's callback:

function createUser (callback) {
  callback(new Error('user exists'));
}

createUser(function (err) {
  expect(err.message).to.equal('user exists')
});

I need to assert that the error is passed.

Is that the best way to do this?

Feel hacky in a way.

[domenic]

It sounds like you're trying to test that a function is invoked with a certain value. That's not entirely within Chai's domain, but more in the domain of a spy library like Sinon.JS. You can use Sinon with the Sinon–Chai plugin to get a pretty nice syntax for making assertions about spy calls:

var spy = sinon.spy();
createUser(spy);

expect(spy).to.have.been.calledWith(new Error("user exists"));

// without Sinon–Chai:
expect(spy.calledWith(new Error("user exists"))).to.be.ok;

[logicalparadox]

@johnnywengluu Were you able to accomplish what you were setting out to do.

As a side note, you can also do the following:

expect(err).to.exist
  .and.be.instanceof(Error)
  .and.have.property('message', 'user exists');

Though, I do agree with @domenic ... if you are doing a lot of this kind of checking you should make it easier on yourself and include the spy libraries.

[ghost]

Nice example.

Right now your code will do it, but I'll look into why I might want to use spy.

Thanks a lot.

Johnny

Sent from my iPad

On 4 jun 2012, at 00:28, Jake [email protected] wrote:

@johnnywengluu Were you able to accomplish what you were setting out to do.

As a side note, you can also do the following:

expect(err).to.exist
 .and.be.instanceof(Error)
 .and.have.property('message', 'user exists');

Though, I do agree with @domenic ... if you are doing a lot of this kind of checking you should make it easier on yourself and include the spy libraries.

---

Reply to this email directly or view it on GitHub:
https://github.com/chaijs/chai/issues/70#issuecomment-6089679

[logicalparadox]

Great. Let us know if you have any more questions.

Closing.