# Property Based Tester

> Generates property-based tests that verify invariants across thousands of randomly generated inputs.

- Skill: `tomevault-io/property-based-tester` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/property-based-tester`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/property-based-tester/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/property-based-tester

---


# Property-Based Tester

Implements property-based testing frameworks that generate random test inputs and verify properties hold, finding edge cases that manual testing misses.

## When to Use This Skill

- Testing algebraic laws (monoid, functor, monad)
- Verifying compiler transformations preserve semantics
- Finding bugs in data structures
- Fuzzing APIs with type-aware generation

## What This Skill Does

1. **Generators**: Builds random generators for types via combinators
2. **Property Definition**: Defines properties as functions returning Boolean
3. **Shrinking**: Implements minimal counterexample finding
4. **Statistics**: Reports distribution of test inputs

## Key Concepts

| Concept | Description |
|---------|-------------|
| Generator | Produces random values of a type |
| Shrinker | Reduces failing inputs to minimal examples |
| Property | Invariant that should hold for all inputs |
| Coverage | Distribution of generated inputs |

## Tips

- Write properties that should always hold, not just examples
- Use shrinking to get minimal failing cases
- Cover edge cases: empty, single element, large inputs
- Combine with type-based generation for better coverage

## Related Skills

- `smt-solver-interface` - Symbolic verification
- `fuzzer-generator` - Random testing
- `type-inference-engine` - Type-aware generation

## Canonical References

| Reference | Why It Matters |
|-----------|----------------|
| **Claessen & Hughes, "QuickCheck: Lightweight Automatic Testing" (ICFP 2000)** | Original Haskell property-based testing library |
| **MacIver, "Hypothesis: Property-Based Testing in Python" (2015+)** | Python ecosystem standard with sophisticated coverage guidance |
| **Claessen & Hughes, "Testing the Hard Stuff and Staying Sane" (ICFP 2002)** | Advanced random testing techniques for critical software |

## Tradeoffs and Limitations

| Approach | Pros | Cons |
|----------|------|------|
| Random generation | Finds edge cases | May miss specific bugs |
| Enumeration | Complete coverage | State space explosion |
| Symbolic execution | Targeted testing | Slower, complex |

## Assessment Criteria

| Criterion | What to Look For |
|-----------|------------------|
| Generator coverage | All interesting cases covered |
| Shrinking effectiveness | Minimal failing examples |
| Property correctness | Properties capture true invariants |

### Quality Indicators

✅ **Good**: Good coverage, effective shrinking, correct properties
⚠️ **Warning**: Limited coverage, slow shrinking
❌ **Bad**: Wrong properties, no shrinking

## Research Tools & Artifacts

Property-based testing frameworks:

| Tool | Language | What to Learn |
|------|----------|---------------|
| **QuickCheck** | Haskell | Original PBT |
| **Hypothesis** | Python | Python standard |
| **Fast-Check** | TypeScript | Composable |
| **ScalaCheck** | Scala | Integration |
| **Erlang QuickCheck** | Erlang | Industrial |

## Research Frontiers

### 1. Stateful Testing
- **Goal**: Test stateful systems
- **Papers**: "QuickCheck Testing for Stateful Software"
- **Tools**: StateMachines, sequences

## Implementation Pitfalls

| Pitfall | Real Consequence | Solution |
|---------|-----------------|----------|
| **Weak properties** | False positives | Strengthen invariants |

---
> Converted and distributed by [TomeVault](https://tomevault.io/claim/rainoftime) — claim your Tome and manage your conversions.
<!-- tomevault:4.0:skill_md:2026-04-11 -->