Refactoring · interview question

If you wrote a test around types during refactors, what should the test prove first?

Multiple choiceHardchapter-10-curatedpremiumrefactoringtypes-during-refactors

python

def build_receipt(order_id: str, subtotal: float, shipping: float) -> str:
    return f"{order_id}:{subtotal + shipping:.2f}"

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 types during refactors.Keep types during refactors 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 types during refactors, what should the test prove first?

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