Security · interview question

If you wrote a test around input validation, what should the test prove first?

Multiple choiceEasychapter-17-curatedpremiumsecurityinput-validation

python

def normalize_order_id(order_id: str) -> str:
    if not order_id.startswith("ORD-"):
        raise ValueError("invalid order id")
    return order_id

That the rule behaves correctly at the boundary cases the lesson is trying to make explicit.Delay clarity until production traffic reveals the edge case and then patch it under pressure.Solve the symptom with comments only and avoid changing the code shape around input validation.Keep input validation implicit so the script stays short and hope the next engineer infers the rule.

Answer and explanation

Correct answer

A. That the rule behaves correctly at the boundary cases the lesson is trying to make explicit.

Why

Good tests make the design safer to change because they lock in the meaningful behavior rather than surface-level implementation details.

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If you wrote a test around input validation, what should the test prove first?

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