Replace assert_template assertions

Let's test the result of the action by inspecting response's body
as @hoffmanc already did for a couple of other tests.

test/functional/pages_controller_test.rb

@@ -8,5 +8,6 @@ def setup
   test 'should get how_to' do
     get :show, params: { id: 'how_to' }
     assert_response :success
+    assert response.body.include? '<h1>How to</h1>'
   end
 end

test/functional/welcome_controller_test.rb

@@ -12,12 +12,28 @@ class WelcomeControllerTest < ActionController::TestCase
   test 'should get index' do
     get :index
     assert_response :success
+    # It includes the public header
+    assert(
+      response.body.include?(
+        'Tomatoes is a Pomodoro Technique<sup>®</sup> driven time tracker'
+      )
+    )
+    # It doesn't include the current user's list of tomatoes
+    assert_not response.body.include? 'Today&#39;s tomatoes'
   end
 
   test 'current user should get index' do
     session[:user_id] = @user.id
 
     get :index
     assert_response :success
+    # It doesn't include the public header
+    assert_not(
+      response.body.include?(
+        'Tomatoes is a Pomodoro Technique<sup>®</sup> driven time tracker'
+      )
+    )
+    # It includes the current user's list of tomatoes
+    assert response.body.include? 'Today&#39;s tomatoes'
   end
 end