add assertion test for router

This test aims to test the ember-routing assertion, specifically:
````
  store: Ember.computed(function(){
    var container = this.container;
    var routeName = this.routeName;
    var namespace = get(this, 'router.namespace');

    return {
      find: function(name, value) {
        var modelClass = container.lookupFactory('model:' + name);

        Ember.assert("You used the dynamic segment " + name + "_id in your route "+ routeName + ", but " + namespace + "." + classify(name) + " did not exist and you did not override your route's `model` hook.", modelClass);

        return modelClass.find(value);
      }
    };
  }),

````