Correctness and Confidence

ArrayList is correct if every operation behaves as the List ADT specifies, for every valid input. Correctness is measured against the contract, not against the code.

It only covers the few inputs the student happened to type, so a bug on any other input goes unnoticed. And the student is the one who judges every printed value, which is slow and easy to get wrong.

No. Correctness requires the right behavior on all valid inputs, and a suite only checks the inputs someone wrote down. Passing tests are evidence of correctness, not proof. Proof would need formal verification.