it works like this:

```javascript
test('xxx', function(done) {
  Contacts.findBy('Grillo', function(contacts) {
    done(function() {
      assert.ok(xxx);
      assert.equal(xxx);
    });
  }
}
```

The function as a parameter of done lets the framework now about the stack trace in case one of the assert throws. This is an addition to mocha that they don't want to upstream.