clarification

Hello, I would like to clarify this task.

The example that baffles me the most - #assert(almostequal(battleprobability(['A', 'D'], 4, 3), 1.0000)), "Always win".

Even if I assume that player 2 never wins, how can we say that the player one wins every single time with certainty, if there is a very small chance of a perpetual no-win, for instance if player 1 throws all Ds all the time (but there are other combination when player 2 does not lose any units).

Am I missing something, or is there a precondition that should be added to the mix?

Thank you.