Problems with Mocha + Mongodb

[pablocodeiro]

I have this little test:

const mongo = require('mongodb').MongoClient;

const dbString = 'mongodb://localhost:27017/tests';

describe("In mongodb", function () {
   beforeEach(function (done) {
      mongo.connect(dbString)
            .then(function (currentDb) {
               done()
            })
            .catch(function (e) {
               done(e)
            });
   });

   it('Empty test', function () {
      return;
   });
});

And this little Bitbucket pipeline

image: node:6.9.4

pipelines:
  default:
    - step:
          services:
            - mongo
          script:
            - npm install
            - npm install -g mocha
            - mocha

definitions:
  services:
    mongo:
      image: mongo

The problem is that the Mocha test never ends! I can see the end:

  1 passing (37ms) 

But the "mocha" action never ends in Bitbucket. In all our computers this works OK.

I found a solution closing the mongodb connection from the tests (i.e. using "after" and doing db.close for each mongo.connect), but I want to know why the behavior of this is different in pipelines and in our computers, and how to solve it without change our tests...