fix(mission_either_one_relation_concern): two relations are also invalid

app/models/concerns/mission_either_one_relation.rb

@@ -23,7 +23,13 @@ module MissionEitherOneRelation
     private
 
     def validate_group_assignment_or_assignment_present
-      errors.add(:association_insuficient) if assignment.blank? && group_assignment.blank?
+      if assignment.blank? && group_assignment.blank?
+        errors.add(:assignment, :insuficient_relation)
+        errors.add(:group_assignment, :insuficient_relation)
+      elsif assignment.present? && group_assignment.present?
+        errors.add(:assignment, :too_many_relations)
+        errors.add(:group_assignment, :too_many_relations)
+      end
     end
   end
 end

config/locales/de.yml

@@ -577,7 +577,8 @@ de:
         semester_process_volunteer_mission:
           attributes:
             assignment: &id-mission-relation-insuficient
-              insuficient_relation: Es wird mindestens ein Assignment oder GroupAssignment benötigt.
+              insuficient_relation: Es wird mindestens ein Assignment oder GroupAssignment benötigt
+              too_many_relations: Es darf nur ein Assignment oder ein GroupAssignment verbunden werden
             group_assignment: *id-mission-relation-insuficient
     models:
       assignment: Begleitung