add unit tests

model/preference.go

@@ -12,6 +12,7 @@ import (
 const (
 	PREFERENCE_CATEGORY_DIRECT_CHANNEL_SHOW = "direct_channel_show"
 	PREFERENCE_CATEGORY_TUTORIAL_STEPS      = "tutorial_step"
+	PREFERENCE_CATEGORY_ADVANCED_SETTINGS   = "advanced_settings"
 )
 
 type Preference struct {