event: refactor as_json method and add a test

spec/models/event_spec.rb

@@ -17,4 +17,27 @@ describe Event do
       expect(event.abstract_word_count).to eq(0)
     end
   end
+
+  describe 'as_json' do
+    let(:event) { create(:event) }
+
+    it 'adds the event\'s room_guid, track_color and length' do
+      event.room = create(:room)
+      event.track = create(:track, color: '#efefef')
+      json_hash = event.as_json(nil)
+
+      expect(json_hash[:room_guid]).to eq(event.room.guid)
+      expect(json_hash[:track_color]).to eq('#efefef')
+      expect(json_hash[:length]).to eq(30)
+    end
+
+    it 'uses correct default values for room_guid, track_color and length' do
+      event.event_type = nil
+      json_hash = event.as_json(nil)
+
+      expect(json_hash[:room_guid]).to be_nil
+      expect(json_hash[:track_color]).to eq('#ffffff')
+      expect(json_hash[:length]).to eq(25)
+    end
+  end
 end