Create MainController with start page action

app/assets/javascripts/application.js

@@ -12,4 +12,4 @@
 //
 //= require rails-ujs
 //= require turbolinks
-//= require_tree .
+//= require_tree ./application

app/assets/javascripts/cable.js

-// Action Cable provides the framework to deal with WebSockets in Rails.
-// You can generate new channels where WebSocket features live using the `rails generate channel` command.
-//
-//= require action_cable
-//= require_self
-//= require_tree ./channels
-
-(function() {
-  this.App || (this.App = {});
-
-  App.cable = ActionCable.createConsumer();
-
-}).call(this);

app/assets/stylesheets/application.css

@@ -10,6 +10,6 @@
  * files in this directory. Styles in this file should be added after the last require_* statement.
  * It is generally better to create a new file per style scope.
  *
- *= require_tree .
+ *= require_tree ./application
  *= require_self
  */

app/controllers/main_controller.rb

+class MainController < ApplicationController
+  def start_page
+  end
+end

app/views/main/start_page.html.haml

+%h1 Main#start_page
+%p Find me in app/views/main/start_page.html.haml

config/routes.rb

 Rails.application.routes.draw do
-  # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
+
+  root 'main#start_page'
+
 end

test/controllers/main_controller_test.rb

+require 'test_helper'
+
+class MainControllerTest < ActionDispatch::IntegrationTest
+  test "should get start_page by root path" do
+    get root_url
+    assert_response :success
+  end
+
+end