property-based-testing-with-kotestlisted

# Property-Based Testing with Kotest ## Workflow: Writing a property-based test 1. **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. 2. **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 **at least two** complementary properties per function under test. 3. **Design generators.** Use `Arb` for random+edge-case generation (default), `Exhaustive` for small finite domains. Constrain generators at construction — don't rely on `filter()` or `assume()` (keep discard rate under 10%). For domain types, compose with `arbitrary { ... }` using `.bind()`. 4. **Write the test.** Use `checkAll` with Kot