Bluebird Promise becomes resolved in any case

Question

I must be doing something wrong, however this is my testcase:

const { describe, it } = require('mocha'),
  should = require('should'),
  Promise = require('bluebird') //v3.4.6
describe('Bluebird', () => {
  it('Promise is never resolved but does it get resolved?', () => {
    new Promise(() => false)
      .should.be.fulfilled() // It really shouldn't be
  })
})

This passes, but shouldn't it fail?

Answer 1

When working with promises in mocha tests, it is important to return the promise from the test.

In your case, that would be:

it('Promise is never resolved but does it get resolved?', () => {
   return new Promise(() => false)
    .should.be.fulfilled()
})

However, that is probably still not exactly what you need here, as the fulfillment of the promise can't be determined at the time should is invoked. Your actual test is probably different, the most important part is still to return the promise chain.

When you do that, then you don't need to further assert the fulfillment/rejection of the promise, as that is done implicitly by mocha.

I'm personally a big fan of chai-as-promised, which would allow you to use the exact same test you had before, but this time, it would be working.