FizzBuzzGame | Practising TDD swift , building a FizzBuzz game | Unit Testing library

For educational purposes I am implementing classical "fizz buzz" problem using multiple threads.

"fizz buzz" game is:

The player designated to go first says the number "1", and each player thenceforth counts one number in turn. However, any number divisible by three is replaced by the word fizz and any divisible by five by the word buzz. Numbers divisible by both become fizz buzz

In my implementation I have 4 threads:

• First thread prints number if it is not multiple of 3 or 5 and increment current counter.
• Second thread prints “fizz”...
• Third thread prints “buzz”...
• Forth thread prints “fizz buzz”...

I don't use any locking and thread synchronizations mechanisms. Is my multi-threaded "fizz buzz" implementation thread safe? And, if not, why? I added comments in code of implementation for "suspicious" places.

My Implementation: