asynchronous throw

[quangv]

What's the best way to test for throw() (great addition btw) asynchronously? using with mocha.

Example...

it('works sync', function() {
  (function() {
    throw {message: 'error'};
  }).should.throw();
});

this works.

it('should throw async', function(done) {
  (function() {
    setTimeout(function() {
      throw {message: 'error'};
    }, 200);
  }).should.throw();
});     

AssertionError: expected an exception to be thrown

[tj]

those callsites will have come and gone so you can't try/catch async stuff, that's why node does callback(err)

[tj]

also: devthought.com/2011/12/22/a-string-is-not-an-error/

you wont want to throw { message: 'here' }, even though it's not a string, same stuff applies

[quangv]

hey TJ, thanks for the link, yeh I still don't know how to read those stacktraces... I should figure that out.

correct me if I'm wrong, but if you throw new Error doesn't mocha just stop and returns?

---

nvm I was wrong

suite 'Test', ->
    test 'throw Error', ->
        (->
            throw new Error 'Cat'
        ).should.throw()

works fine... reason i thought so was because I was having trouble using .should.throw() with superagent (detecting failure) but maybe it's more to do with it being async...

var request = require('superagent');

it('tests connection failure', function(done) {
  (function() {
    request.get('blahblah', function(res) {
      res.status.should.eql(200);
      done();
    });
  }).should.throw();
});

  AssertionError: expected an exception to be thrown

excuse the coffee-script... hope you don't mind, I was too lazy to copy/paste into cs compiler :)

[tj]

what do you mean? you dont know how to read stack traces? but the thing is that exceptions just "unwind" the stack, so when you're in a callback from something async it's not the same stack anymore so try/catch doesn't work

[quangv]

Error
    at Object.<anonymous> (/private/tmp/error.js:2:11)
    at Object.<anonymous> (/dir/errorLoop.coffee:6:4)
    at Module._compile (node.js:462:23)

might be cause I predominantly use coffee-script, but those :2:11 never matches up for me lol... so I usually disregard the error outputs...

[tj]

ah.. yeah that would be coffeescript for you lol aren't you glad it's so helpful

[quangv]

hah... yes... but coffee has it's perks... !