property-test-generator

Design and generate property-based tests for changed files, with self-scoring to ensure quality (24/30+ on the evaluation rubric).

Filter to source files (.ts, .tsx, .js, .jsx, .py, .rs), excluding test files, config, styles, and assets.

| Invariant | Output always satisfies a condition | Length preservation, range bounds, type guarantees | | Round-trip | decode(encode(x)) === x | Parsers, serializers, codecs | | Idempotence | f(f(x)) === f(x) | Normalizers, formatters, canonicalizers | | Metamorphic | Relationship between f(x) and f(transform(x)) | Sort, filter, math operations |

Design and generate property-based tests (PBT) for changed files in the current git branch. Extracts specifications, designs properties (invariants, round-trip, idempotence, metamorphic, monotonicity, reference model), builds generator strategies, implements tests, and self-scores against a rubric (24/30+ required). Supports fast-check (TS/JS), hypothesis (Python), and proptest (Rust). Use when: (1) "write property tests for my changes", (2) "add PBT", (3) "property-based test", (4) after implementing pure functions, validators, parsers, or formatters to verify invariants. Source: nimiusrd/agent-skills.