How to check assertion error in Mocha when testing async code

Question

When testing async code with Mocha and one of my asserts fails, all Mocha does is to report a timeout error. Is there a way to improve this? How to know what asserts failed and why?

mocha

  Contact
    #getContacts()
      1) should return at least 1 contact


  0 passing (3s)
  1 failing

  1) Contact #getContacts() should return at least 1 contact:
     Error: timeout of 3000ms exceeded. Ensure the done() callback is being called in this test.

Code:

var assert         = require("assert");
var contact        = require("../lib/contact.js");
var chai           = require('chai');
var should         = chai.should();

describe('Contact', function() {
  describe('#getContacts()', function() {
    it('should return at least 1 contact', function(done) {
      contact.getContacts().then(function(contacts) {
        assert.equal(4,2)

        done()
      });
    })
  })
});

Answer 1

The issue is that the assertion fails, which throws an exception. This causes the promise to be rejected, but there isn't anyone to notice. Your code only checks if the promise succeeds. If you return the promise, then mocha will check for it and fail the test if the promise is rejected.

So you want

it('should return at least 1 contact', function() {
    return contact.getContacts().then(function(contacts) {
      assert.equal(4,2);
    });
}); 

Answer 2

You should return the promise like this:

it('should return at least 1 contact', function() {
  return contact.getContacts().then(function(contacts) {
    assert.equal(4,2);
  });
});