If I understand the docs correctly, the following should work:

const PubSub = require('@google-cloud/pubsub');
const Promise = require('bluebird');

const pubsubClient = PubSub({
  projectId: 'some-project-1234',
  promise: Promise
});

pubsubClient.createTopic('test')
  .tap(console.log);

... but it throws with TypeError: pubsubClient.createTopic(...).tap is not a function, since the returned promise is a native one and not by bluebird.

Setting global.Promise to bluebird makes this example work, but that's besides the point.

I also tried setting it in the option object of the call to createTopic(), but that also fails.

Looking at common/utils, the promise option does not make it into the context of promisfy() there.

Environment details

• OS: macOs 10.13.2
• Node.js version: 9.2.1
• npm version: 5.6.0
• @google-cloud/pubsub version: 0.16.0