testing failed promises with mocha's built-in promise support

javascript, mocha.js, node.js, promise

Solution

Some more digging, and it appears the right way is to add an additional catch block, like so...

it.only("do something (negative test)", function (done) {

  var Q = require('q');

  function makePromise() {
    var deferred = Q.defer();
    deferred.reject(Error('fail'));
    return deferred.promise;
  };

  makePromise()
  .catch(function(e) {
    expect(e.message).to.equal('fail');
  })
  .then(done, done);

});

I'm interested in alternative ideas, or confirmation that this is fine the way it is.. thanks.

UPDATE:

Ben - I now grok what you were saying, esp. after the terse but helpful comment from Benjamin G.

To summarize:

When you pass in a `done` parameter, the test is expected to trigger it's 'done-ness' by calling the `done()` function;

When you don't pass in a `done` parameter, it normally only works for synchronous calls. However, if you return a promise, the mocha framework (mocha >1.18) will catch any failures that normally would have been swallowed (per the promises spec). Here is an updated version:

it.only("standalone neg test for mocha+promises", function () {

  var Q = require('q');

  function makePromise() {
    var deferred = Q.defer();
    deferred.reject(Error('fail'));
    return deferred.promise;
  };

  return makePromise()
  .catch(function(e) {
    expect(e.message).to.equal('fail');
  });

});

Problem

Original source

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