Here is the stack trace:

/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:320
self.s.pool = new Pool(Object.assign(self.s.options, options, {bson: this.s.
^
TypeError: undefined is not a function
at Server.connect (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:320:33)
at Server.connect (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/lib/server.js:328:17)
at open (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/lib/db.js:220:19)
at Db.open (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/lib/db.js:243:44)
at connectFunction (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/lib/mongo_client.js:220:67)
at connect (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/lib/mongo_client.js:367:5)
at Function.MongoClient.connect (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongodb/lib/mongo_client.js:113:3)
at clientify (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongo-clean/index.js:47:17)
at Holder.work (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongo-clean/node_modules/steed/node_modules/fastfall/fall.js:103:23)
at Object.fall [as waterfall] (/home/travis/build/mcollina/mqemitter-mongodb/node_modules/mongo-clean/node_modules/steed/node_modules/fastfall/fall.js:30:13)
not ok 1 no plan found