Domain Modeling · interview question

If you wrote a test around instance methods, what should the test prove first?

Multiple choiceMediumchapter-7-curatedpremiumdomain-modelinginstance-methods

python

from dataclasses import dataclass

@dataclass
class OrderLine:
    unit_price: float
    quantity: int

    def line_total(self) -> float:
        return self.unit_price * self.quantity

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

Answer and explanation

Correct answer

C. 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 instance methods, what should the test prove first?

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