>>> from sabateria2 import modifica_stock

>>> stock =[[30, 4], [45, 5], [36, 8], [37, 12], [42, 6], [32, 8], \
... [34, 9], [41, 4], [38, 6], [44, 7], [33, 8], [40, 5], [35, 7], [39, 12], \
... [29, 9], [31, 5]]
>>> entrades = [[36, 1], [37, 2], [28, 3], [32, 1], [41, 4], [43, 2]]
>>> modifica_stock(stock, entrades)
>>> stock == [[30, 4], [45, 5], [36, 9], [37, 14], [42, 6], [32, 9], \
... [34, 9], [41, 8], [38, 6], [44, 7], [33, 8], [40, 5], [35, 7], [39, 12],\
... [29, 9], [31, 5], [28, 3], [43, 2]]
True