I am really sorry. The issue was in my solution.

The tests pass randomly as the order of threads depends on their id which can vary

It's not clear for me what happens on the 3rd cycle? All of them drink 4 cans of cola or they continue drinking 2 cans at once? Is this a correct queue?

Sheldon, Leonard, Penny, Rajesh, Howard,
Sheldon, Sheldon, Leonard, Leonard, Penny, Penny, Rajesh, Rajesh, Howard, Howard,
Sheldon, Sheldon, Sheldon, Sheldon, Leonard, Leonard, Leonard, Leonard, Penny, Penny, Penny, Penny, ...

If I am not mistaken // operator is in Python since 2.2... I found this in PEP 238

Here are the changes 2.2 introduces:

A new operator, //, is the floor division operator. (Yes, we know it looks like C++'s comment symbol.) // always performs floor division no matter what the types of its operands are, so 1 // 2 is 0 and 1.0 // 2.0 is also 0.0.

// is always available in Python 2.2; you don't need to enable it using a __future__ statement.