User unsubscribed on Q&A topic shouldn’t get email notification when user leave comment on his question

Pre-condition:
1. User1 should be created and logged
2. User1 should have VIEW_TOPICS and CREATE_POST permissions
3. At least one branch created
4. A branch has Q&A topic
5. User1 should be subscribed on Q&A topic and unsubscribe on branch
6. User1 is author of Q&A topic