coffee_sean_version.coffee

 routesTo: (url, route_name)->
      visit(url)
      andThen ->
        current_route = App.__container__.lookup('controller:application').currentRouteName
        equal current_route, route_name, "Expected #{route_name}, got: #{current_route}"

javascript_output_sean_version.js

({
  routesTo: function(url, route_name) {
    visit(url);
    return andThen(function() {
      var current_route;
      current_route = App.__container__.lookup('controller:application').currentRouteName;
      return equal(current_route, route_name, "Expected " + route_name + ", got: " + current_route);
    });
  }
});

/* Basically what's happening is coffeescripit is returning an unnamed object with a routesTo function
*  This would not make the helper available in the tests.
*/

js2coffee_original_output.coffee

routesTo = (url, route_name) ->
  visit url
  andThen ->
    current_route = AddressBook.__container__.lookup("controller:application").currentRouteName
    equal current_route, route_name, "Expected " + route_name + ", got: " + current_route
    return

  return
  
# Note that when it is transpiled from the original, two return keywords are added, which are missing from your version

original_book.js

var routesTo = function (url, route_name) {
    visit(url);
    andThen(function () {
        var current_route = AddressBook.__container__.lookup('controller:application').currentRouteName;
        equal(current_route, route_name, 'Expected ' + route_name + ', got: ' + current_route);
    });
};