def test_adding_to_inventory():
vendor = Vendor()
item = "new item"
result = vendor.add(item)
assert len(vendor.inventory) == 1
assert item in vendor.inventory
assert result == item
def test_adding_to_inventory():
#arrange
vendor = Vendor()
item = "new item"
#act
result = vendor.add(item)
#assert
assert len(vendor.inventory) is 1
assert item in vendor.inventory
assert result is item
def test_different_vendors_inventories_are_siloed():
vendor1 = Vendor()
vendor2 = Vendor()
vendor1.add("item1")
assert vendor1.inventory == ["item1"]
assert vendor2.inventory == []
