new ItemTest
rename getPromotions to generatePromotions
add can_get_arguments_value test
new CartItemTest
add can_get_arguments value
add can_get_subTotal test
new promotionCalculatorTest
add can_caLculate_buy_two_get_one_free_promotion test
add can_caLculate_second_half_price_promotion test
add can_calculator_discount_promotion test
new ScannerTest
add can_getInputs test
new cartTest
delete useless codes
add can_set_cartItems
delete inputs and items arguments
delete useless codes
modify public to private
modify format
new for format