Isn't there a mistake with the following assertion?

assert divide_pie((-1, -1, -1))) == (8, 27)

To me, the result should be as follows:
1st robot: 6/6 - 1/6 = 5/6
2nd robot: 5/6 - (5/61/6) = 30/36 - 5/36 = 25/36
3rd robot: 25/36 - (25/361/6) = 150/216 - 25/216 = 125/216