regenerate friendly id as needed

app/models/challenge.rb

@@ -86,6 +86,16 @@ def cache_rendered_markdown
     end
   end
 
+  def reset_friendly_id
+    if challenge_changed?
+      self.slug = 'poo'
+    end
+  end
+
+  def should_generate_new_friendly_id?
+    challenge_changed?
+  end
+
 
   def valid_status
     if self.status == :running

spec/models/challenge_spec.rb

@@ -122,6 +122,15 @@
       end
     end
 
+    describe "friendly_id" do
+      it 'updates the slug when the challenge title changes' do
+        challenge = create(:challenge)
+        challenge.challenge = 'a new challenge title'
+        challenge.save!
+        expect(challenge.slug).to eq('a-new-challenge-title')
+      end
+    end
+
 
   end
 end