Debugging: the introduction

A user added six different books to their shopping cart. They applied the discount code SAVE10 to the last item, but the discount was not applied.

A user added The Small Web and Testing Tiny Apps to the cart. At checkout, the dollar total did not make sense.

A user added Git Without Panic with the discount code SAVE10. Later, they added another copy. The discount is now gone.

A user added APIs for Beginners and CSS That Behaves to the cart. Later, they tried to remove the first book, but the second one was removed instead.