Writing a simple automation test in node.js but having trouble with sync calls

I am trying to write an automation script to test some of my api calls here is a simple example:

async.series([
    function(callback){
       func.clean_database()
       callback(null);     
    },
    function(callback){
       func.register_and_auth(users[0])
       callback(null);   
    }
],
function(err, results){
    console.log('done');
});

Clean database could look as simple as:

clean_database: function () { 
    var Projects = mongoose.model("Projects", new mongoose.Schema({}));
    Projects.collection.remove(function (err, results) { console.log("Emptied: Projects"); });
    return true;
},

The problem is that the register_and_auth(users[0]) runs before the cleaning database has completed.. thus telling me the user has already registered. I was under the impression async.series would run these in series i.e. one after the other.

How can I make it so that the callback(null) is tied to the completion of the function i am running in the first step?

Thanks!

::::UPDATE::::

If anyone cares I had to extend this and call more methods to mimic a user flow here is what it ultimately looks like.. if anyone wants to improve upon this please do

async.series([    
  func.clean_database, function(one_callback){
    func.register_and_auth(users[0], function(callback) {
      console.log('-- Starting Create and Upload');
      func.auth_and_create_project_and_upload(users[0], data, function(callback) { 
        console.log('-- Starting Annotations');
        func.auth_open_project_add_annotations_to_all_pages(users[0], annotation, function(callback) { 
          console.log('-- Done with User 0.');
          one_callback();
        });
      });
    });
  },
  function(two_callback) {
    func.register_and_auth(users[1], function(callback) {
      console.log('-- Starting Create and Upload');
      func.auth_and_create_project_and_upload(users[1], data, function(callback) { 
        console.log('-- Starting Annotations');
        func.auth_open_project_add_annotations_to_all_pages(users[1], annotation, function(callback) { 
            console.log('-- Done with User 1.');
            two_callback();
          });
        });
      });
    },
  ],
  function(err, results){
  console.log('Load test complete for two users.');   
});