# Behavior Contract

> - "Positive amounts still process correctly"

- Skill: `gabrielmoreira/behavior-contract` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add gabrielmoreira/behavior-contract`
- Raw SKILL.md: https://api.skillmd.com/api/skills/gabrielmoreira/behavior-contract/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: gabrielmoreira (https://skillmd.com/u/gabrielmoreira)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/gabrielmoreira/behavior-contract

---


- "Positive amounts still process correctly"
- "Negative amounts still throw `InvalidAmountError`"
- "Receipt format remains unchanged for all amount types"

## Contract Document Template

```markdown
# Behavior Contract: [Bug Title]

## Bug Condition
[Precise description of triggering conditions]

## Postcondition
[Expected correct behavior after fix]

## Invariants
- [ ] Invariant 1: [existing behavior to preserve]
- [ ] Invariant 2: [existing behavior to preserve]

## Testable Assertions
1. `expect(processPayment(0)).toEqual({ amount: 0, status: 'completed' })`
2. `expect(processPayment(100)).toEqual({ amount: 100, status: 'completed' })`
3. `expect(() => processPayment(-1)).toThrow(InvalidAmountError)`
```

## Usage in Bugfix Workflow

1. Bug analysis identifies root cause at file:line
2. This skill formalizes the contract from the analysis
3. tdd-enforcer writes failing test from Bug Condition
4. tdd-enforcer writes preservation tests from Invariants
5. Minimal fix applied, contract audited