Feature to fail invalid async tests

[mfulton26]

Mocha has an async-only option to "force all tests to take a callback (async) or return a promise". This is very handy as it protects developers from creating tests that always pass regardless of the expect statements. e.g.:

Always passes:

it('should have a link to Protractor's website', () => {
  expect(anchor.getAttribute('href')).toEqual('http://www.protractortest.org/#/');
});

Passes whenever the expect statement passes:

it('should have a link to Protractor's website', () => {
  return expect(anchor.getAttribute('href')).toEqual('http://www.protractortest.org/#/');
});

All it takes is that missing return keyword.

I propose adding a feature similar to Mocha's (perhaps even enabled by default) to force each it to receive a done argument or to return a promise.

Or, if possible, it would be great to simply have some kind of lint check that runs to confirm that there aren't any ignored promises.