Testing Property Based

Testing Property-Based

Overview

Use this skill to validate invariants beyond hand-picked test cases by combining generators, shrinking, and reproducible seeds.

Scope Boundaries

• Use when input space is large and example-based tests are insufficient.
• Typical requests:
  • Verify encode/decode roundtrip invariants for arbitrary inputs.
  • Stress aggregate invariants with generated data.
  • Catch edge cases that fixed examples miss.
• Do not use when:
  • A small deterministic unit test set is sufficient (testing-unit).
  • The primary scope is UI journey validation (testing-e2e).

Inputs

• Invariants and domain constraints
• Generator strategy and seed reproducibility requirements
• Runtime budget and flaky-risk tolerance

Outputs

• Property definitions and generator coverage strategy
• Decision record for shrinking and seed policy
• Verification checklist with failing-case reproduction guidance

Workflow

1. Formalize invariants and invalid-state assumptions.
2. Design generators that reflect realistic and adversarial inputs.
3. Compare generation/shrinking strategies and choose one.
4. Run property tests with reproducible seeds.
5. Triages failures with shrunk counterexamples and publish fixes.

Quality Gates

• Core invariants are explicit and testable.
• Generators cover edge and adversarial shapes.
• Failures are reproducible via seed and shrunk case.
• Residual unknowns are documented.

Failure Handling

• Stop when invariants are undefined or contradictory.
• Escalate when generator quality is too weak for meaningful coverage.

Bundled Resources

• references/trigger-and-examples.md: trigger patterns, anti-patterns, and deliverable expectations.