property-based-testing

What this skill does

Guides property-based testing (PBT) across Python, Rust, JavaScript/TypeScript, Solidity, and Go to surface security-relevant edge cases that example-based unit tests systematically miss. Rather than asserting that specific inputs produce specific outputs, PBT defines invariants the system must always satisfy — then lets a framework generate hundreds or thousands of inputs to try to break them. This skill covers property identification, framework selection, test writing, counterexample minimization, and failure triage with a focus on overflow/underflow, deserialization roundtrips, access control invariants, and state machine violations.

When to use

• When auditing cryptographic primitives, parsers, or serialization libraries for correctness under adversarial input
• When reviewing smart contracts for arithmetic invariants before or alongside a formal audit
• When a function has a large or unbounded input domain that example tests cannot adequately cover
• When debugging a known crash and needing a minimal reproducible input automatically
• When adding regression coverage to a function that previously had a security-relevant bug

Prerequisites

Install the framework for the target language:

Python — Hypothesis

pip install hypothesis
# Optional: pytest integration
pip install pytest hypothesis

Rust — proptest

# Cargo.toml
[dev-dependencies]
proptest = "1"

JavaScript / TypeScript — fast-check

npm install --save-dev fast-check
# or
yarn add --dev fast-check

Solidity — Foundry fuzz testing

curl -L https://foundry.paradigm.xyz | bash
foundryup

Go — testing/quick (stdlib)

import "testing/quick"
// No additional installation required

Inputs

Variable	Required	Description
PBT_TARGET_FILE	required	Path to the source file or contract under test
PBT_LANGUAGE	required	Target language: python, rust, js, solidity, go
PBT_ITERATIONS	optional	Number of test cases to generate (default: framework default, typically 100)
PBT_OUTPUT_DIR	optional	Directory to save failing counterexamples (default: ./pbt-output)
PBT_SEED	optional	Fixed seed for reproducible runs