do not render the development environment for exercises without visible files

app/controllers/exercises_controller.rb

@@ -82,6 +82,7 @@ class ExercisesController < ApplicationController
   private :handle_file_uploads
 
   def implement
+    redirect_to(@exercise, alert: t('exercises.implement.no_files')) unless @exercise.files.visible.exists?
     @submission = current_user.submissions.where(exercise_id: @exercise.id).order('created_at DESC').first
     @files = (@submission ? @submission.collect_files : @exercise.files).select(&:visible).sort_by(&:name_with_extension)
     @paths = collect_paths(@files)

app/views/application/_flash.html.slim

@@ -1,3 +1,3 @@
 #flash data-message-failure=t('shared.message_failure')
-  - %w[danger info notice success warning].each do |severity|
-    p.alert.flash class="alert-#{severity == 'notice' ? 'success' : severity}" id="flash-#{severity}" = flash[severity]
+  - %w[alert danger info notice success warning].each do |severity|
+    p.alert.flash class="alert-#{{'alert' => 'warning', 'notice' => 'success'}.fetch(severity, severity)}" id="flash-#{severity}" = flash[severity]

config/locales/de.yml

@@ -199,6 +199,7 @@ de:
       feedback: Feedback
       file: 'Test-Datei <span class="number">%{number}</span> (<span class="filename">%{filename}</span>)'
       hint: Tipp
+      no_files: Die Aufgabe umfasst noch keine sichtbaren Dateien.
       no_output: Die letzte Code-Ausführung hat keine Ausgabe erzeugt.
       no_output_yet: Bisher existiert noch keine Ausgabe.
       output: Programm-Ausgabe

config/locales/en.yml

@@ -199,6 +199,7 @@ en:
       feedback: Feedback
       file: 'Test File <span class="number">%{number}</span> (<span class="filename">%{filename}</span>)'
       hint: Hint
+      no_files: The exercise does not comprise visible files yet.
       no_output: The last code run has not generated any output.
       no_output_yet: There is no output yet.
       output: Program Output

spec/controllers/exercises_controller_spec.rb

@@ -146,12 +146,15 @@ describe ExercisesController do
 
   describe 'GET #implement' do
     let(:request) { proc { get :implement, id: exercise.id } }
+
+    context 'with an exercise with visible files' do
+      let(:exercise) { FactoryGirl.create(:fibonacci) }
       before(:each) { request.call }
 
       expect_assigns(exercise: :exercise)
 
       context 'with an existing submission' do
-      let!(:submission) { FactoryGirl.create(:submission, exercise_id: exercise.id, user_id: user.id, user_type: InternalUser.class.name) }
+        let!(:submission) { FactoryGirl.create(:submission, exercise_id: exercise.id, user_id: user.id, user_type: user.class.name) }
 
         it "populates the editors with the submission's files' content" do
           request.call
@@ -169,6 +172,15 @@ describe ExercisesController do
       expect_template(:implement)
     end
 
+    context 'with an exercise without visible files' do
+      before(:each) { request.call }
+
+      expect_assigns(exercise: :exercise)
+      expect_flash_message(:alert, :'exercises.implement.no_files')
+      expect_redirect(:exercise)
+    end
+  end
+
   describe 'GET #index' do
     let(:scope) { Pundit.policy_scope!(user, Exercise) }
     before(:all) { FactoryGirl.create_pair(:dummy) }