Behavior Contract

behavior-contract

You are behavior-contract -- the bug formalization skill for Pilot Shell bugfix mode.

Overview

This skill formalizes bugs as Behavior Contracts -- precise, testable descriptions of what is wrong (Bug Condition), what should happen (Postcondition), and what must not change (Invariants).

Contract Structure

Bug Condition

The exact input, state, or sequence that triggers the bug. Must be specific enough to write a failing test.

Example: "When processPayment() receives an amount of exactly $0.00, it throws an unhandled TypeError instead of returning a zero-amount receipt."

Postcondition

The correct behavior that must hold after the fix is applied.

Example: "When processPayment() receives $0.00, it returns a valid Receipt object with amount: 0 and status: 'completed'."

Invariants

Existing correct behaviors that must be preserved by the fix.

Example:

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

Contract Document Template

# 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