📦 deps(thirdparty): update snapshots

2026-05-29 08:33:53 +00:00
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+# TDD Session: Bug Fix
+
+TDD workflow for fixing a production bug with test reproduction first.
+
+## Bug Report
+
+**Issue**: Division by zero crashes calculator service
+**Reporter**: User reported 500 error when calculating percentage with zero total
+**Stack Trace**:
+
+```
+Error: Division by zero
+  at calculatePercentage (calculator.ts:45)
+  at handler (api/stats.ts:23)
+```
+
+**Priority**: High — causes service crash
+
+## TDD Workflow
+
+### Task Setup
+
+```text
+1. Write failing test reproducing bug [in_progress]
+2. Fix bug with minimal code [pending]
+3. Refactor if needed [pending]
+4. Verify fix [pending]
+```
+
+## RED Phase: Reproduce Bug (4 min)
+
+Confidence: `▓▓░░░` → Can reproduce, know the fix
+
+First, understand the current implementation:
+
+**Read**: `src/calculator/percentage.ts`
+
+```typescript
+export function calculatePercentage(value: number, total: number): number {
+  return (value / total) * 100
+}
+```
+
+Issue clear: No validation for zero total.
+
+**Write failing test**: `src/calculator/percentage.test.ts`
+
+```typescript
+import { describe, test, expect } from 'bun:test'
+import { calculatePercentage } from './percentage'
+
+describe('calculatePercentage', () => {
+  // Existing tests
+  test('calculates percentage correctly', () => {
+    expect(calculatePercentage(25, 100)).toBe(25)
+    expect(calculatePercentage(50, 200)).toBe(25)
+  })
+
+  // NEW: Bug reproduction test
+  test('handles division by zero gracefully', () => {
+    const result = calculatePercentage(10, 0)
+
+    expect(result).toBe(0)
+    // OR throw error approach:
+    // expect(() => calculatePercentage(10, 0)).toThrow('Total cannot be zero')
+  })
+
+  test('handles zero value with valid total', () => {
+    expect(calculatePercentage(0, 100)).toBe(0)
+  })
+})
+```
+
+**Run test**: `bun test percentage.test.ts`
+
+```
+calculatePercentage
+  ✓ calculates percentage correctly
+  ✗ handles division by zero gracefully
+    Expected: 0
+    Received: Infinity
+  ✓ handles zero value with valid total
+
+1 failing
+```
+
+Bug reproduced successfully — test fails as expected.
+
+**Commit**: `test: add failing test for division by zero bug`
+
+**Task Update**:
+
+```text
+1. Write failing test reproducing bug [completed]
+2. Fix bug with minimal code [in_progress]
+3. Refactor if needed [pending]
+4. Verify fix [pending]
+```
+
+## GREEN Phase: Fix Bug (3 min)
+
+Confidence: `▓▓▓▓░` → Know exact fix needed
+
+**Update**: `src/calculator/percentage.ts`
+
+```typescript
+export function calculatePercentage(value: number, total: number): number {
+  // Fix: Handle division by zero
+  if (total === 0) {
+    return 0
+  }
+
+  return (value / total) * 100
+}
+```
+
+**Run tests**: `bun test percentage.test.ts`
+
+```
+calculatePercentage
+  ✓ calculates percentage correctly
+  ✓ handles division by zero gracefully
+  ✓ handles zero value with valid total
+
+3 passing
+```
+
+All tests pass — bug fixed.
+
+**Verify no regressions**: `bun test`
+
+```
+All test suites passing (23 tests total)
+```
+
+No other tests broken — safe fix.
+
+**Commit**: `fix: handle division by zero in percentage calculation`
+
+**Task Update**:
+
+```text
+1. Write failing test reproducing bug [completed]
+2. Fix bug with minimal code [completed]
+3. Refactor if needed [in_progress]
+4. Verify fix [pending]
+```
+
+## REFACTOR Phase: Consider Improvements (5 min)
+
+Current fix works but could be more robust. Consider:
+
+1. Should negative totals be handled?
+2. Should we return error instead of 0?
+3. Type safety improvements?
+
+**Decision**: Add input validation, use Result type for better error handling.
+
+**Refactored**: `src/calculator/percentage.ts`
+
+```typescript
+type PercentageResult =
+  | { type: 'success'; value: number }
+  | { type: 'error'; code: 'ZERO_TOTAL' | 'NEGATIVE_TOTAL' }
+
+export function calculatePercentage(
+  value: number,
+  total: number
+): PercentageResult {
+  // Validate total
+  if (total === 0) {
+    return { type: 'error', code: 'ZERO_TOTAL' }
+  }
+
+  if (total < 0) {
+    return { type: 'error', code: 'NEGATIVE_TOTAL' }
+  }
+
+  return {
+    type: 'success',
+    value: (value / total) * 100,
+  }
+}
+```
+
+**Update tests** to match new signature:
+
+```typescript
+describe('calculatePercentage', () => {
+  test('calculates percentage correctly', () => {
+    const result1 = calculatePercentage(25, 100)
+    const result2 = calculatePercentage(50, 200)
+
+    expect(result1).toEqual({ type: 'success', value: 25 })
+    expect(result2).toEqual({ type: 'success', value: 25 })
+  })
+
+  test('returns error for division by zero', () => {
+    const result = calculatePercentage(10, 0)
+
+    expect(result).toEqual({
+      type: 'error',
+      code: 'ZERO_TOTAL',
+    })
+  })
+
+  test('returns error for negative total', () => {
+    const result = calculatePercentage(10, -100)
+
+    expect(result).toEqual({
+      type: 'error',
+      code: 'NEGATIVE_TOTAL',
+    })
+  })
+
+  test('handles zero value with valid total', () => {
+    const result = calculatePercentage(0, 100)
+
+    expect(result).toEqual({ type: 'success', value: 0 })
+  })
+})
+```
+
+**Run tests**: `bun test percentage.test.ts`
+
+```
+calculatePercentage
+  ✓ calculates percentage correctly
+  ✓ returns error for division by zero
+  ✓ returns error for negative total
+  ✓ handles zero value with valid total
+
+4 passing
+```
+
+**Update usage** in `api/stats.ts`:
+
+```typescript
+// Before
+const percentage = calculatePercentage(completed, total)
+return { percentage }
+
+// After
+const result = calculatePercentage(completed, total)
+if (result.type === 'error') {
+  return { error: 'Invalid calculation', code: result.code }
+}
+return { percentage: result.value }
+```
+
+**Run all tests**: `bun test`
+
+```
+All tests passing (24 tests total)
+```
+
+No regressions — refactor successful.
+
+**Commit**: `refactor: use Result type for percentage calculation errors`
+
+**Task Update**:
+
+```text
+1. Write failing test reproducing bug [completed]
+2. Fix bug with minimal code [completed]
+3. Refactor if needed [completed]
+4. Verify fix [in_progress]
+```
+
+## VERIFY Phase: Comprehensive Validation (4 min)
+
+Run full test suite with coverage:
+
+```bash
+bun test --coverage
+```
+
+```
+Coverage Summary:
+  percentage.ts: 100% statements, 100% branches
+
+All tests passing (24 total)
+```
+
+Run mutation testing on updated code:
+
+```bash
+bun x stryker run --mutate "src/calculator/percentage.ts"
+```
+
+```
+Mutation Score: 100%
+All mutants killed
+
+Mutations tested:
+  ✓ === → !== (killed by "returns error for division by zero")
+  ✓ < → <= (killed by "returns error for negative total")
+  ✓ / → * (killed by "calculates percentage correctly")
+  ✓ 0 → 1 (killed by "handles zero value with valid total")
+```
+
+Perfect mutation score — tests thoroughly verify behavior.
+
+**Integration test** to verify API fix:
+
+```typescript
+describe('GET /api/stats', () => {
+  test('handles zero total gracefully', async () => {
+    const response = await request(app)
+      .get('/api/stats')
+      .query({ completed: 10, total: 0 })
+
+    expect(response.status).toBe(200)
+    expect(response.body).toMatchObject({
+      error: 'Invalid calculation',
+      code: 'ZERO_TOTAL',
+    })
+  })
+})
+```
+
+**Run integration tests**: `bun test tests/integration/`
+
+```
+API Integration Tests
+  ✓ handles zero total gracefully
+
+All integration tests passing
+```
+
+**Task Update**:
+
+```text
+1. Write failing test reproducing bug [completed]
+2. Fix bug with minimal code [completed]
+3. Refactor if needed [completed]
+4. Verify fix [completed]
+```
+
+## Session Summary
+
+**Duration**: 16 minutes total
+- RED: 4 min
+- GREEN: 3 min
+- REFACTOR: 5 min
+- VERIFY: 4 min
+
+**Bug**: Division by zero crash
+**Fix**: Added validation with Result type
+**Tests**: 4 new tests + 1 integration test
+**Coverage**: 100% on changed code
+**Mutation Score**: 100%
+
+**Improvements beyond minimal fix**:
+- Used discriminated union for error handling
+- Added negative total validation
+- Updated API to handle error results
+- Added integration test
+
+**Production deployment**:
+- All tests passing
+- No regressions detected
+- Error handling verified
+- Ready to deploy
+
+## Key TDD Bug Fix Principles
+
+1. **RED first**: Always reproduce bug with failing test before fixing
+2. **Minimal GREEN**: Fix the immediate issue first
+3. **Refactor for robustness**: Improve error handling and edge cases
+4. **Verify thoroughly**: Run full suite + mutation tests + integration tests
+5. **Document in test**: Test name describes the bug being fixed
+
+## Anti-patterns Avoided
+
+Avoided jumping straight to fix without test:
+
+```typescript
+// ❌ Wrong approach
+// 1. See bug report
+// 2. Add if (total === 0) return 0
+// 3. Deploy and hope
+
+// ✓ Correct TDD approach
+// 1. Write failing test reproducing bug
+// 2. Verify test fails
+// 3. Add minimal fix
+// 4. Verify test passes
+// 5. Refactor for robustness
+// 6. Verify with mutation testing
+```
+
+Avoided over-engineering initial fix:
+
+```typescript
+// ❌ Too complex for first fix
+if (total === 0 || total < 0 || !isFinite(total) || isNaN(total)) {
+  throw new ValidationError(...)
+}
+
+// ✓ Minimal fix first (GREEN phase)
+if (total === 0) {
+  return 0
+}
+
+// ✓ Then refactor with proper error handling (REFACTOR phase)
+if (total === 0) {
+  return { type: 'error', code: 'ZERO_TOTAL' }
+}
+```
+
+## Commit History
+
+```
+test: add failing test for division by zero bug
+fix: handle division by zero in percentage calculation
+refactor: use Result type for percentage calculation errors
+```
+
+Clean, focused commits showing TDD progression.