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

Property-based testing generates random inputs and verifies properties hold for all inputs, rather than testing specific examples. Properties: invariants, round-trip (encode-decode), oracle (compare implementations), inductive (recursive properties). Tools: QuickCheck (Haskell), Hypothesis (Python), jqwik (Java), fast-check (JS). Benefits: finds edge cases, more thorough coverage, reveals assumptions. Challenges: defining good properties, debugging failures (shrinking helps). Use for: parsers, serialization, algorithms, mathematical properties. Complements example-based tests.