agent-bank: Skill for OpenCode

What I Do

Ensure every feature you build is testable from the start. This skill teaches:

1. Testing pyramid (fast → slow)
2. API exposure patterns for testability
3. Local testing setup
4. Integration with staging tests
5. When to use each testing layer

Core Philosophy

"If you can't test it locally, you can't test it."

Every feature should be testable at multiple levels. Design for testability, don't bolt it on later.

---

Testing Pyramid

From fastest (run constantly) to slowest (run occasionally):

                    ▲
                   /U\        UI Tests (E2E)
                  / I \       - Browser automation
                 /-----\      - Run on staging only
                / API   \     API/Integration Tests
               / TESTS   \    - tRPC procedures
              /-----------\   - Can run locally
             /   UNIT      \  Unit Tests
            /    TESTS      \ - Pure functions
           /------------------\ - Fastest, run always

Layer	Speed	Where	When to Use
Unit	<1s	Local	Pure logic, utils, calculations
API/Integration	1-10s	Local + CI	tRPC, DB operations, business logic
Staging	30s-2m	Vercel preview	Full flow verification
UI/E2E	2-5m	Staging only	Critical user journeys

---

Layer 1: Unit Tests (Fastest)

When to Use

• Pure functions with no side effects
• Calculations, formatting, validation
• Business logic that doesn't touch DB/APIs

Pattern

// packages/web/src/lib/utils/calculate-fee.ts
export function calculateFee(amount: number, feePercent: number): number {
  return amount * (feePercent / 100);
}

// packages/web/src/lib/utils/calculate-fee.test.ts
import { describe, it, expect } from 'vitest';
import { calculateFee } from './calculate-fee';

describe('calculateFee', () => {
  it('calculates 1% fee correctly', () => {
    expect(calculateFee(1000, 1)).toBe(10);
  });

  it('handles zero amount', () => {
    expect(calculateFee(0, 5)).toBe(0);
  });
});