app/controllers/application_controller.rb

@@ -1,9 +1,3 @@
 class ApplicationController < ActionController::Base
-  before_action :authenticate_user
-
-  private
-
-  def authenticate_user
-    Current.user = User.find_by(id: session[:current_user_id])
-  end
+  include Authenticatable
 end

app/controllers/concerns/authenticatable.rb

@@ -0,0 +1,13 @@
+module Authenticatable
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :authenticate_user
+  end
+
+  private
+
+  def authenticate_user
+    Current.user = User.find_by(id: session[:current_user_id])
+  end
+end

test/system/sessions_test.rb

@@ -17,6 +17,14 @@ class SessionsTest < ApplicationSystemTestCase
   end
 
   test "should destroy Session" do
+    visit new_session_url
+
+    fill_in "Email", with: @user.email
+    fill_in "Password", with: "secret"
+
+    click_on "Create Session"
+    assert_text "Session was successfully created"
+
     visit root_url
     click_on "Log out", match: :first