Meteorjs, when writing unit tests, I cann't create a user with Accounts.createUser in lib folder

When writing my unit tests in lib folder, I'm trying to create a user, but after try several options, it never creates the user.

I've already tried with

 if(Meteor.isClient){

    Accounts.createUser({......})

 }

and after that loggin

Meteor.loginWithPassword(.....)

it creates, but when I go out of that conditional, the user disappear, does someone has a clue what it could be? please, really I need the user created in lib before continue running my unit tests(to work in both client and server side). It supposed lib load first and works for client and server side :(