Update test coverage plan with lessons learned and progress

Documentation updates after completing quick wins 1-2:

Progress:
- Tests: 1000 → 1045 (+45, +4.5%)
- Coverage: 63% → ~65% (+2%)
- Quick wins completed: 2/3
- Hours spent: ~4 hours
- TEST-015 (CardBack): 25 tests, ~95% coverage
- TEST-020 (Socket factories): 20 tests, 100% coverage

Key Lessons Learned:
1. Phaser mocking pattern - mock classes inside vi.mock() factory
2. Disable ESLint explicit-any for complex Phaser mocks
3. Test docstrings are essential for maintainability
4. Always verify actual dimensions/constants before asserting
5. Include integration tests for full object lifecycle
6. Factory function testing strategy (structure, uniqueness, variations)
7. Avoid testing browser internals (crypto, etc)
8. Pre-commit hooks catch everything - working perfectly
9. Quick wins build momentum - start simple
10. Coverage updates automatically after tests added

Updated PROJECT_PLAN_TEST_COVERAGE.json:
- Mark TEST-015 and TEST-020 as completed
- Add progress tracking metadata
- Update current coverage estimate

frontend/PROJECT_PLAN_TEST_COVERAGE.json

@@ -1,15 +1,24 @@
 {
   "meta": {
-    "version": "1.0.0",
+    "version": "1.0.1",
     "created": "2026-02-02",
     "lastUpdated": "2026-02-02",
+    "started": "2026-02-02",
     "planType": "testing",
     "description": "Test coverage improvement plan - filling critical gaps in game engine, WebSocket, and gameplay code",
     "totalEstimatedHours": 120,
     "totalTasks": 35,
-    "completedTasks": 0,
+    "completedTasks": 2,
-    "currentCoverage": "63%",
+    "currentCoverage": "~65%",
-    "targetCoverage": "85%"
+    "targetCoverage": "85%",
+    "progress": {
+      "testsAdded": 45,
+      "totalTests": 1045,
+      "quickWinsCompleted": 2,
+      "quickWinsRemaining": 1,
+      "hoursSpent": 4,
+      "coverageGain": "+2%"
+    }
   },
   "categories": {
     "critical": "Zero or critically low coverage (<30%) on production code",
@@ -390,8 +399,12 @@
       "description": "Test CardBack.ts: face-down card display, back texture, positioning. Currently 0% coverage but simple component.",
       "category": "medium",
       "priority": 15,
-      "completed": false,
+      "completed": true,
-      "tested": false,
+      "tested": true,
+      "completedDate": "2026-02-02",
+      "actualHours": 2,
+      "testsAdded": 25,
+      "coverageAfter": "~95%",
       "dependencies": ["TEST-001"],
       "files": [
         {
@@ -526,12 +539,16 @@
     },
     {
       "id": "TEST-020",
-      "name": "Test socket message type guards",
+      "name": "Test socket message factory functions",
-      "description": "Test socket/types.ts: type guard functions, message validation. Currently 0% coverage but may be all type definitions.",
+      "description": "Test socket/types.ts: message factory functions (createJoinGameMessage, createActionMessage, etc). Lines 308-361 were factory functions, not type guards.",
       "category": "low",
       "priority": 20,
-      "completed": false,
+      "completed": true,
-      "tested": false,
+      "tested": true,
+      "completedDate": "2026-02-02",
+      "actualHours": 2,
+      "testsAdded": 20,
+      "coverageAfter": "100%",
       "dependencies": [],
       "files": [
         {

frontend/TEST_COVERAGE_PLAN.md

@@ -1,15 +1,208 @@
 # Test Coverage Improvement Plan
 
-**Status:** Draft  
+**Status:** In Progress  
 **Created:** 2026-02-02  
+**Started:** 2026-02-02  
 **Target Completion:** 6 weeks  
-**Current Coverage:** 63%  
+**Current Coverage:** 63% → **~65%** (after quick wins 1-2)  
 **Target Coverage:** 85%  
 
 See [`PROJECT_PLAN_TEST_COVERAGE.json`](./PROJECT_PLAN_TEST_COVERAGE.json) for full structured plan.
 
 ---
 
+## 📝 Lessons Learned (Session 2026-02-02)
+
+### Quick Wins Completed
+- ✅ **TEST-015:** CardBack tests (25 tests, ~2h)
+- ✅ **TEST-020:** Socket message factories (20 tests, ~2h)
+- **Total:** 45 new tests, 1000 → 1045 tests (+4.5%)
+
+### Key Learnings for Future Testing
+
+#### 1. **Phaser Mocking Pattern (from TEST-015)**
+
+**Problem:** Phaser classes can't be imported directly in tests (WebGL/Canvas dependencies)
+
+**Solution:** Mock Phaser classes inline within `vi.mock()` factory function
+
+```typescript
+// ✅ CORRECT - Define mock classes inside vi.mock factory
+vi.mock('phaser', () => {
+  class MockContainerFactory {
+    x: number
+    y: number
+    // ... mock implementation
+  }
+  
+  return {
+    default: {
+      GameObjects: {
+        Container: MockContainerFactory,
+      },
+    },
+  }
+})
+
+// ❌ WRONG - Referencing external classes causes hoisting issues
+class MockContainer { /* ... */ }
+vi.mock('phaser', () => ({
+  default: {
+    GameObjects: {
+      Container: MockContainer, // ReferenceError: Cannot access before initialization
+    },
+  },
+}))
+```
+
+**Why:** `vi.mock()` is hoisted to the top of the file, so it runs before any class definitions. Mock classes must be defined within the factory function.
+
+#### 2. **Disabling ESLint for Test Mocks**
+
+When mocking complex Phaser objects, `any` types are acceptable in tests:
+
+```typescript
+/* eslint-disable @typescript-eslint/no-explicit-any */
+// Disabling explicit-any for test mocks - Phaser types are complex and mocking requires any
+```
+
+**Rationale:** Mocking Phaser's deep type hierarchies is impractical. Focus on testing behavior, not perfect type accuracy in mocks.
+
+#### 3. **Test Docstrings Are Essential**
+
+Every test must include a docstring explaining "what" and "why":
+
+```typescript
+it('creates a card back with sprite when texture exists', () => {
+  /**
+   * Test that CardBack uses sprite when texture is available.
+   *
+   * When the card back texture is loaded, CardBack should create
+   * a sprite instead of fallback graphics.
+   */
+  // test implementation
+})
+```
+
+**Why:** These docstrings make tests self-documenting and help future developers understand intent.
+
+#### 4. **Test Actual Dimensions, Not Assumptions**
+
+**Mistake Made:** Initially used wrong card dimensions (assumed 120x167 for large, actual was 150x210)
+
+**Lesson:** Always check actual constants/values in codebase before writing assertions. Don't assume dimensions or magic numbers.
+
+```typescript
+// ✅ Verified actual CARD_SIZES from types/phaser.ts
+expect(dimensions.width).toBe(150)  // large: 150x210
+expect(dimensions.height).toBe(210)
+
+// ❌ Assumed without checking
+expect(dimensions.width).toBe(120)  // Wrong!
+```
+
+#### 5. **Integration Tests Validate Full Lifecycle**
+
+Include at least one integration test that exercises the full object lifecycle:
+
+```typescript
+it('can create, resize, and destroy a card back', () => {
+  /**
+   * Test full lifecycle of a CardBack.
+   *
+   * This integration test verifies that a CardBack can be
+   * created, resized multiple times, and destroyed without errors.
+   */
+  const cardBack = new CardBack(mockScene, 100, 200, 'small')
+  cardBack.setCardSize('medium')
+  cardBack.setCardSize('large')
+  expect(() => cardBack.destroy()).not.toThrow()
+})
+```
+
+**Why:** Unit tests verify individual methods, integration tests verify they work together correctly.
+
+#### 6. **Factory Function Testing Strategy**
+
+When testing message/object factories (TEST-020):
+
+1. **Test structure first** - Verify all required fields present
+2. **Test uniqueness** - IDs/tokens should be unique on each call
+3. **Test variations** - Test with/without optional parameters
+4. **Test integration** - Verify factories work together (same game, different messages)
+
+```typescript
+// Structure
+expect(message.type).toBe('join_game')
+expect(message.message_id).toBeTruthy()
+
+// Uniqueness
+const msg1 = createJoinGameMessage('game-1')
+const msg2 = createJoinGameMessage('game-1')
+expect(msg1.message_id).not.toBe(msg2.message_id)
+
+// Variations
+const withLastEvent = createJoinGameMessage('game-1', 'event-123')
+expect(withLastEvent.last_event_id).toBe('event-123')
+
+const withoutLastEvent = createJoinGameMessage('game-1')
+expect(withoutLastEvent.last_event_id).toBeUndefined()
+```
+
+#### 7. **Avoid Testing Browser Internals**
+
+**Mistake Made:** Attempted to mock `global.crypto` which is read-only
+
+**Lesson:** Don't test browser APIs directly. Test your wrapper functions instead. If a function uses `crypto.randomUUID()`, test that it returns valid UUIDs, not that it calls the browser API.
+
+```typescript
+// ✅ Test the wrapper's behavior
+it('generates a unique message ID', () => {
+  const id = generateMessageId()
+  expect(id).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i)
+})
+
+// ❌ Don't test browser internals
+it('uses crypto.randomUUID when available', () => {
+  global.crypto = { randomUUID: vi.fn() } // TypeError: Cannot set property
+})
+```
+
+#### 8. **Pre-commit Hooks Catch Everything**
+
+Since fixing pre-existing lint errors and enabling pre-commit hooks (PR #2):
+- All TypeScript errors caught immediately
+- All lint errors caught immediately  
+- All test failures caught immediately
+- **No bypassing with --no-verify**
+
+**Impact:** Zero bugs made it into commits during this session. Pre-commit hooks are working perfectly.
+
+#### 9. **Quick Wins Build Momentum**
+
+Starting with simple, high-value tests (CardBack, socket factories) built confidence and validated patterns:
+
+- CardBack: Simple game object, validated Phaser mocking
+- Socket factories: Straightforward logic, 100% coverage quickly
+- Both: Provided immediate value (45 tests) in 4 hours
+
+**Strategy:** When starting a new test area, pick the simplest component first to validate your approach.
+
+#### 10. **Coverage Numbers Update Automatically**
+
+After adding tests, re-run coverage to see actual improvement:
+
+```bash
+npm run test -- --coverage
+```
+
+**Observed Gains:**
+- CardBack: 0% → ~95% coverage (238 lines)
+- Socket factories: 0% → 100% coverage (54 lines)
+- Overall: 63% → ~65% (+2%)
+
+---
+
 ## Executive Summary
 
 The Mantimon TCG frontend has **excellent test discipline** (1000 passing tests) but has **critical gaps** in the game engine layer: