fuzz-testing-designer

Purpose

Design coverage-guided fuzz testing harnesses and property-based tests (AFL, libFuzzer, Atheris, Go native testing.F, fast-check) that generate millions of pseudo-random, adversarial inputs to discover buffer overflows, unhandled panics, assertion failures, and infinite loops.

When to Use

• Testing data parsers (JSON, XML, YAML, binary protocols, image decoders).
• Validating cryptographic algorithms, compilers, and serialization engines.
• Securing untrusted user input handlers against malicious exploit payloads.

What to Analyze

1. Fuzz Target Entry Point: Minimal, deterministic function signature accepting byte slices or structured objects.
2. Seed Corpus: High-quality initial valid samples to guide mutation algorithms toward deeper code paths.
3. Property Invariants: Assertions that must hold true for any input (e.g. deserialize(serialize(x)) == x, no unhandled panics, execution completes in <100ms).
4. Sanitizers: AddressSanitizer (ASan), MemorySanitizer (MSan), and UndefinedBehaviorSanitizer (UBSan).
5. Crash Minimization: Replay and minimization script for discovered failure artifacts.

Output Format

• Fuzz Test Harness Code: Complete test harness in Go (F.Fuzz), TypeScript (fast-check), Python (Atheris), or Rust (cargo-fuzz).
• Property Invariants Specification: Mathematical or logical invariants asserted.
• Corpus & Crash Reproducer Guide: Instructions to reproduce and minimize crashes.

Avoid

• Performing expensive disk I/O or network calls inside the inner fuzz loop (kills execution throughput).
• Fuzzing non-deterministic code containing random seeds or system timers.