Testinghard

What is property-based testing and when would you use it?

Tags

#property-based#invariants#testing

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Answer

Property-based testing checks general properties over many generated inputs rather than fixed examples. It’s useful for edge cases and complex logic.

Advanced answer

Deep dive

Focus on invariants:

Define properties (commutativity, idempotency, monotonicity).
Generate inputs and shrink failing cases.
Complements unit tests by finding unexpected edge cases.

Examples

Sorting property:

For any list L: sort(L) is ordered and contains same elements

Common pitfalls

Weak properties that don’t catch real bugs.
Unbounded generators causing slow tests.
Ignoring shrinked counterexamples.

Interview follow-ups

How do you choose good properties?
What is shrinking and why is it important?
When is property-based not worth it?

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