modify test productDao
add test  should_return_75_when_input_productId method
modify getDiscount method
add test should_return_75_when_input_productId
modify getDiscount
modify getDiscount
modify getMoney method
format code
modify printInventory method
delete useless test
modify test should_return_12_when_input_cartItem
modify test should_return_a_product_list
delete useless setter method
delete useless method
delete useless files
add CategoryServiceTest
add test should_return_category_when_input_productId method
modify getCategory method
refactor ProductService
modify test should_return_75_when_input_productId