Stock Up The Inventory

An Inventory keeps a dict attribute stock that maps an item name to a quantity. Write the body of add: when item is already a key, add quantity to its value; otherwise create the key with quantity as its value. Do NOT write a main block or any top-level test code; the tests construct the class. Input: two lines, an item name and a whole-number quantity, which the tests read and pass to add on an inventory that already holds 3 apples; the tests then print each item and its quantity on one line, in alphabetical order.