Admin Controller

class Admin::ApplicationController < ApplicationController
  before_action :authorize_admin!
  
  def index
    @users = User.all
    @forums = Forum.all
  end
  
  private
  
  def authorize_admin!
    authenticate_user!
    
    unless current_user.admin?
      redirect_to root_path, alert: "You are not allowed to do that."
    end
  end
end

Admin Index View

<header>
  <h1>Admin's Lounge, Please enjoy your stay!</h1>
</header>

<br>
<div class='row'>
  <div class='col-md-6'>
    <h3>List of Users:</h3>
    <% @users.each do |user| %>
      <ul class='attributes'>
        <li><%= link_to user.email, admin_user_path(user) %></li>
      </ul>
    <% end %>
    <%= link_to 'New User', new_admin_user_path, class: "btn btn-primary" %>
  </div>
  
  <div class='col-md-6'>
    <h3>List of Forums:</h3>
    <% @forums.each do |forum| %>
      <ul class='attributes'>
        <li><%= link_to forum.title, forum_path(forum) %></li>
      </ul>
    <% end %>
    <%= link_to 'New Forum', new_admin_forum_path, class: "btn btn-primary" %>
  </div>
</div>

error message

mfifth:~/workspace $ bundle exec rspec
.F...

Failures:

  1) Administrators can successfully update existing users
     Failure/Error: <% @forums.each do |forum| %>
     
     ActionView::Template::Error:
       undefined method `each' for nil:NilClass
     # ./app/views/admin/application/index.html.erb:19:in `_app_views_admin_application_index_html_erb__3305476992675424763_47925760'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/warden-1.2.6/lib/warden/manager.rb:35:in `block in call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/warden-1.2.6/lib/warden/manager.rb:34:in `catch'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/warden-1.2.6/lib/warden/manager.rb:34:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/etag.rb:24:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/conditionalget.rb:25:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/head.rb:13:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/session/abstract/id.rb:225:in `context'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/session/abstract/id.rb:220:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/railties-4.2.5/lib/rails/rack/logger.rb:38:in `call_app'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/railties-4.2.5/lib/rails/rack/logger.rb:20:in `block in call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/railties-4.2.5/lib/rails/rack/logger.rb:20:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/methodoverride.rb:22:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/runtime.rb:18:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/lock.rb:17:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/sendfile.rb:113:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/railties-4.2.5/lib/rails/engine.rb:518:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/railties-4.2.5/lib/rails/application.rb:165:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/urlmap.rb:66:in `block in call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/urlmap.rb:50:in `each'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-1.6.4/lib/rack/urlmap.rb:50:in `call'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-test-0.6.3/lib/rack/mock_session.rb:30:in `request'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-test-0.6.3/lib/rack/test.rb:244:in `process_request'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/rack-test-0.6.3/lib/rack/test.rb:58:in `get'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/rack_test/browser.rb:61:in `process'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/rack_test/browser.rb:39:in `block in process_and_follow_redirects'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/rack_test/browser.rb:38:in `times'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/rack_test/browser.rb:38:in `process_and_follow_redirects'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/rack_test/browser.rb:27:in `submit'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/rack_test/form.rb:78:in `submit'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/rack_test/node.rb:62:in `click'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/node/element.rb:135:in `block in click'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/node/base.rb:85:in `synchronize'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/node/element.rb:135:in `click'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/node/actions.rb:40:in `click_button'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/session.rb:699:in `block (2 levels) in <class:Session>'
     # /usr/local/rvm/gems/ruby-2.3.0/gems/capybara-2.7.1/lib/capybara/dsl.rb:52:in `block (2 levels) in <module:DSL>'
     # ./spec/features/admin_privileges_spec.rb:28:in `block (2 levels) in <top (required)>'
     # ------------------
     # --- Caused by: ---
     # NoMethodError:
     #   undefined method `each' for nil:NilClass
     #   ./app/views/admin/application/index.html.erb:19:in `_app_views_admin_application_index_html_erb__3305476992675424763_47925760'

Finished in 1.59 seconds (files took 9.98 seconds to load)
5 examples, 1 failure

Failed examples:

rspec ./spec/features/admin_privileges_spec.rb:22 # Administrators can successfully update existing users

mfifth:~/workspace $ 

RSpec Test

require 'rails_helper'

RSpec.describe "Administrators can" do
  let(:admin) { FactoryGirl.create(:user, :admin) }
  let!(:user) { FactoryGirl.create(:user) }
  
  before do
    login_as(admin)
    visit admin_root_path
  end
  
  scenario "successfully create new forums" do
    click_link "New Forum"
    fill_in "Title", with: "Sports"
    fill_in "Description", with: "A place where users can grovel and snicker at each other over
    sports they have absolutely nothing to do with."
    click_button "Create Forum"
    
    expect(page).to have_content "New forum has been created."
  end
  
  scenario 'successfully update existing users' do
    click_link user.email
    click_link "Edit User"
    
    fill_in "Email", with: "[email protected]"
    fill_in "Password", with: "frostedflakes"
    click_button "Update User"
    
    expect(page).to have_content "User has been updated."
  end
end

users controller

class Admin::UsersController < Admin::ApplicationController
  before_action :set_user, only: [:update, :destroy, :show, :edit]
  before_action :authorize_admin!
  
  def index
    @users = User.all
  end
  
  def new
    @user = User.new
  end
  
  def create
    @user = User.new(user_params)
    if @user.save
      flash[:notice] = "User has been successfully created."
      redirect_to admin_users_path
    else
      flash.now[:alert] = "User has not been created."
      render 'new'
    end
  end
  
  def update
    @forums = Forum.all
    
    if @user.update(user_params)
      flash[:notice] = "User has been successfully updated."
      redirect_to admin_users_path
    else
      flash.now[:alert] = "User has not been updated."
      render 'edit'
    end
  end
  
  def destroy
    @user.destroy
    
    flash[:notice] = "User has been deleted."
    redirect_to admin_users_path
  end
  
  def edit
  end
  
  def show
  end
  
  private
  
  def authorize_admin!
    unless current_user.admin?
      redirect_to root_path, alert: "You must be an admin to do that."
    end
  end
  
  def set_user
    @user = User.find(params[:id])
  end
  
  def user_params
    params.require(:user).permit(:email, :password, :admin)
  end
end