How do I check correctness?

Short explanation:

Correctness means the implementation satisfies the required behavior for valid, invalid and concurrent inputs. A review begins with the intended rule, because readable or compilable code can still implement the wrong rule. Trace the inputs, state changes and outputs before judging style.

Key points:

• Compare code with the required behavior, including empty and invalid inputs.

• Trace state changes and check return values.

• Ask whether concurrent requests can break the rule.

• Write down an invariant such as “stock cannot become negative” and look for a path that violates it.

Interview point:

• Explain the failing input or interleaving clearly enough that another developer can reproduce the problem.