Name: Property Based Testing With Kotest
Author: msewell

Workflow: Writing a property-based test

Decide if PBT fits. Use PBT for functions with broad input spaces, clear invariants, round-trip operations, or many parameter combinations. Keep example-based tests for specific business scenarios and regression pinning.
Identify properties. Pick from these patterns (most to least common):
- Roundtrip — decode(encode(x)) == x. For serialize/parse/compress pairs.
- Invariant — a measurable property is preserved (e.g., sort preserves size and elements).
- Idempotence — f(f(x)) == f(x). For trim, distinct, upsert, PUT.
- Oracle — compare optimized implementation against a simple correct one.
- Hard to prove, easy to verify — check output validity (e.g., prime factors multiply back).
- Commutativity — different operation orders yield same result.
- Induction — base case + recursive step.
- Metamorphic — when correct output is unknown, test relationships between outputs under related inputs. Always identify complementary properties per function under test.

Decide if PBT fits. Use PBT for functions with broad input spaces, clear invariants, round-trip operations, or many parameter combinations. Keep example-based tests for specific business scenarios and regression pinning.
Identify properties. Pick from these patterns (most to least common):
- Roundtrip — decode(encode(x)) == x. For serialize/parse/compress pairs.
- Invariant — a measurable property is preserved (e.g., sort preserves size and elements).
- Idempotence — f(f(x)) == f(x). For trim, distinct, upsert, PUT.
- Oracle — compare optimized implementation against a simple correct one.
- Hard to prove, easy to verify — check output validity (e.g., prime factors multiply back).
- Commutativity — different operation orders yield same result.
- Induction — base case + recursive step.
- Metamorphic — when correct output is unknown, test relationships between outputs under related inputs. Always identify complementary properties per function under test.

Property Based Testing With Kotest