---

name: genotoxic description: "Graph-informed mutation testing triage. Parses codebases with Trailmark, runs mutation testing and necessist, then uses survived mutants, unnecessary test statements, and call graph data to identify false positives, missing test coverage, and fuzzing targets. Use when triaging survived mutants, analyzing mutation testing results, identifying test gaps, finding fuzzing targets from weak tests, running mutation frameworks (including circomvent and cairo-mutants), or using necessist."

Genotoxic

Combines mutation testing and necessist (test statement removal) with code graph analysis to triage findings into actionable categories: false positives, missing unit tests, and fuzzing targets.

When to Use

• After mutation testing reveals survived mutants that need triage
• Identifying where unit tests would have the highest impact
• Finding functions that need fuzz harnesses instead of unit tests
• Prioritizing test improvements using data flow context
• Filtering out harmless mutants from actionable ones
• Finding unnecessary test statements that indicate weak assertions (necessist)

When NOT to Use

• Codebase has no existing test suite (write tests first)
• Pure documentation or configuration changes
• Single-file scripts with trivial logic

Prerequisites

• trailmark installed — if uv run trailmark fails, run:

  uv tool install trailmark
  

Python snippets: uv run --with trailmark python - (a tool env is not importable)

**DO NOT** fall back to "manual verification" or "manual analysis"
as a substitute for running trailmark. Install it first. If installation
fails, report the error instead of switching to manual analysis.
- A **mutation testing framework** for the target language — if the framework
command fails (not found, not installed), install it using the instructions
in [references/mutation-frameworks.md](references/mutation-frameworks.md).
**DO NOT** fall back to "manual mutation analysis" or skip mutation testing.
Install the framework first. If installation fails, report the error
instead of switching to manual mutation analysis.
- **necessist** (optional, recommended) — if the target language is
supported (Go, Rust, Solidity/Foundry, TypeScript/Hardhat,
TypeScript/Vitest, Rust/Anchor), install with `cargo install necessist`.
See [references/mutation-frameworks.md](references/mutation-frameworks.md)
for details.
- An existing test suite that passes
- **macOS environment**: Run `ulimit -n 1024` before any `mull-runner`
invocation. macOS Tahoe (26+) sets unlimited file descriptors by
default, which crashes Mull's subprocess spawning. See
[references/mutation-frameworks.md](references/mutation-frameworks.md)
for details.

---

## Rationalizations to Reject

| Rationalization | Why It's Wrong | Required Action |
|-----------------|----------------|-----------------|
| "All survived mutants need tests" | Many are harmless or equivalent | Triage before writing tests |
| "Mutation testing is too noisy" | Noise means you're not triaging | Use graph data to filter |
| "Unit tests cover everything" | Complex data flows need fuzzing | Check entrypoint reachability |
| "Dead code mutants don't matter" | Dead code should be removed | Flag for cleanup |
| "Low complexity = low risk" | Boundary bugs hide in simple code | Check mutant location |
| "Tool isn't installed, I'll do it manually" | Manual analysis misses what tooling catches | Install the tool first |
| "Necessist isn't mutation testing, skip it" | Necessist finds what mutation testing misses: weak tests | Run both when the language supports it |

---

## Quick Start

```bash
# 1. Build the code graph
uv run trailmark analyze --language auto --summary {targetDir}

# 2. Run mutation testing (language-dependent)
# Python:
uv run mutmut run --paths-to-mutate {targetDir}/src
uv run mutmut results

# 2b. Run necessist (if language supported)
necessist

# 3. Analyze results with this skill's workflow (Phase 3)

---

Workflow Overview

Phase 1: Graph Build      → Parse codebase with trailmark
      ↓
Phase 2: Mutation Run     → Execute mutation testing framework
Phase 2b: Necessist Run   → Remove test statements (optional, parallel)
      ↓
Phase 3: Triage           → Classify findings using graph data
      ↓
Output: Categorized Report
  ├── Corroborated         (both tools flag same function — highest value)
  ├── False Positives      (harmless, skip)
  ├── Missing Tests        (write unit tests)
  └── Fuzzing Targets      (set up fuzz harnesses)

---

Decision Tree

├─ Need to set up mutation testing for a language?
│  └─ Read: references/mutation-frameworks.md
│
├─ Need to set up necessist or find weak test statements?
│  └─ Read: references/mutation-frameworks.md (Necessist section)
│
├─ Need to understand the triage criteria in depth?
│  └─ Read: references/triage-methodology.md
│
├─ Need to understand how graph data informs triage?
│  └─ Read: references/graph-analysis.md
│
└─ Already have results + graph? Use Phase 3 below.

---

Phase 1: Build Code Graph and Run Pre-Analysis

Parse the target codebase with trailmark and run pre-analysis before mutation testing. Pre-analysis computes blast radius, entry points, privilege boundaries, and taint propagation, which Phase 3 uses for triage.

uv run trailmark analyze --language auto --summary {targetDir}

Use the QueryEngine API to build the graph and run pre-analysis:

1. QueryEngine.from_directory("{targetDir}", language="auto")
2. Call engine.preanalysis() — mandatory before triage
3. Export with engine.to_json() for cross-referencing with mutation results

If auto-detection is wrong for the target, rerun with an explicit language or comma-separated list such as python,rust.

See references/graph-analysis.md for the full API: node mapping, reachability queries, blast radius, and pre-analysis subgraph lookups.

---

Phase 2: Run Mutation Testing

Select and run the appropriate framework. See references/mutation-frameworks.md for language-specific setup.

Capture survived mutants. Each framework reports differently, but extract these fields per mutant:

| Field | Description | |-------|-------------| | File path | Source file containing the mutant | | Line number | Line where mutation was applied | | Mutation type | What was changed (operator, value, etc.) | | Status | survived, killed, timeout, error |

Filter to survived mutants only for Phase 3.

---

Phase 2b: Run Necessist (Optional)

If the target language is supported (Go, Rust, Solidity/Foundry, TypeScript/Hardhat, TypeScript/Vitest, Rust/Anchor), run necessist to find unnecessary test statements. This runs independently of Phase 2 and can execute in parallel.

# Auto-detect framework
necessist

# Or target specific test files
necessist tests/test_parser.rs

# Export results
necessist --dump

Filter to findings where the test passed after removal. See references/mutation-frameworks.md for framework-specific configuration and the normalized record format.

Map each removal to a production function using the algorithm in references/graph-analysis.md.

---

Phase 3: Triage Findings

For each survived mutant and each necessist removal, determine its triage bucket using graph data. Necessist removals must first be mapped to a production function (see references/graph-analysis.md).

Quick Classification (Mutation Testing)

| Signal | Bucket | Reasoning | |--------|--------|-----------| | No callers in graph | False Positive | Dead code, mutant is unreachable | | Only test callers | False Positive | Test infrastructure, not production | | Logging/display string | False Positive | Cosmetic, no behavioral impact | | Equivalent mutant | False Positive | Behavior unchanged despite mutation | | Simple function, low CC, no entrypoint path | Missing Tests | Unit test is straightforward | | Error handling path | Missing Tests | Should have negative test cases | | Boundary condition (off-by-one) | Missing Tests | Property-based test candidate | | Pure function, deterministic | Missing Tests | Easy to test, high value | | High CC (>10), entrypoint reachable | Fuzzing Target | Complex + exposed = fuzz it | | Parser/validator/deserializer | Fuzzing Target | Structured input handling | | Many callers (>10) + moderate CC | Fuzzing Target | High blast radius | | Binary/wire protocol handling | Fuzzing Target | Fuzzers excel at format testing |

Quick Classification (Necessist)

| Signal | Bucket | Reasoning | |--------|--------|-----------| | Redundant setup or debug call | False Positive | Statement genuinely unnecessary | | Cannot map to production function | False Positive | No graph context for triage | | Call removed, no assertion checks its effect | Missing Tests | Test has weak assertions | | Assertion removed, test still passes | Missing Tests | Redundant or insufficient coverage | | Maps to high-CC entrypoint-reachable function | Fuzzing Target | Complex + exposed + weak test |

When both mutation testing and necessist flag the same production function, mark as corroborated — highest confidence finding.

For detailed criteria, see references/triage-methodology.md.

Graph Queries for Triage

For each mutant, map it to its containing graph node and use pre-analysis subgraphs (tainted, high_blast_radius, privilege_boundary) from Phase 1 to classify it. The classification logic checks: no callers → false positive, privilege boundary → fuzzing, high CC + tainted → fuzzing, high blast radius → fuzzing, otherwise → missing tests.

See references/graph-analysis.md for the batch_triage implementation and node mapping functions.

---

Output Format

Generate a markdown report:

# Genotoxic Triage Report

## Summary
- Total survived mutants: N
- Total necessist removals: N
- Corroborated findings: N
- False positives: N (N%)
- Missing test coverage: N (N%)
- Fuzzing targets: N (N%)

## Corroborated Findings
| File | Line | Function | Mutation Signal | Necessist Signal | Action |
|------|------|----------|----------------|------------------|--------|

## False Positives
| File | Line | Mutation | Reason | Source |
|------|------|----------|--------|--------|

## Missing Test Coverage
| File | Line | Function | CC | Callers | Suggested Test | Source |
|------|------|----------|----|---------|----------------|--------|

## Fuzzing Targets
| File | Line | Function | CC | Entrypoint Path | Blast Radius | Source |
|------|------|----------|----|-----------------|--------------|--------|

The Source column is mutation, necessist, or corroborated.

Write the report to GENOTOXIC_REPORT.md in the working directory.

---

Quality Checklist

Before delivering:

• [ ] Trailmark graph built for target language
• [ ] Mutation framework ran to completion
• [ ] Necessist ran (if language supported) or noted as not applicable
• [ ] All survived mutants triaged (none unclassified)
• [ ] All necessist removals triaged (if applicable)
• [ ] Corroborated findings identified (if both tools ran)
• [ ] False positives have clear justifications
• [ ] Missing test items include suggested test type
• [ ] Fuzzing targets include entrypoint paths and blast radius
• [ ] Report file written to GENOTOXIC_REPORT.md
• [ ] User notified with summary statistics

---

Integration

trailmark skill:

• Phase 1: Build code graph, query complexity and entrypoints
• Phase 3: Caller analysis, reachability, blast radius

property-based-testing skill:

• Missing test coverage items involving boundary conditions
• Roundtrip/idempotenc