Add user: A
Add user: B
Add user: C
A -> add friend -> B
A -> add friend -> C
A and B are already friends
A's friend: B C
A -> remove friend -> B
A and B are not yet friends
B's friend:
A -> send message -> B : Hello World!
B -> receive message -> A : Hello World!
C -> send message -> B : Hello, I'm C.
B -> receive message -> C : Hello, I'm C.
Chat B:
>> From A:
>> Hello World!
>> From C:
>> Hello, I'm C.
Remove user: B
B not in chat
B not in chat
B not in chat
B not in chat
B not in chat
B not in chat
B not in chat