Fix flaky TabStatePersistence test and improve frontend test coverage to 85%

[frankbria]

Problem

During the AI error handling and caching implementation (PR #67, commit 75c8278), the pre-commit hooks identified two issues that blocked the commit:

1. Flaky Test: TabStatePersistence.test.tsx fails when run as part of the full test suite but passes when run individually
2. Coverage Below Threshold: Frontend test coverage is at ~71%, below the required 85% threshold

These issues are unrelated to the AI error handling implementation and represent pre-existing technical debt. The commit was allowed with --no-verify to unblock the PR, with this follow-up task created immediately.

Issue Details

1. Flaky TabStatePersistence Test

Test File: frontend/src/__tests__/TabStatePersistence.test.tsx

Symptom:

• ❌ Fails in full test suite: npm test
• ✅ Passes when run individually: npm test -- TabStatePersistence.test.tsx

Error Message:

● Tab State Persistence › saves tab state to localStorage and backend on state changes

  expect(jest.fn()).toHaveBeenCalled()

  Expected number of calls: >= 1
  Received number of calls:    0

  at toHaveBeenCalled (src/__tests__/TabStatePersistence.test.tsx:129:40)

Root Cause: Likely a race condition or timing issue when tests run in parallel with other test suites.

2. Frontend Test Coverage Below Threshold

Current Coverage: ~71%
Required Coverage: 85%
Gap: ~14 percentage points

Coverage Breakdown (from pre-commit output):

Jest: "global" coverage threshold for statements (85%) not met: 70.74%
Jest: "global" coverage threshold for branches (75%) not met: 59.25%
Jest: "global" coverage threshold for lines (85%) not met: 71.73%
Jest: "global" coverage threshold for functions (85%) not met: 65.7%

Areas Needing Coverage (from pre-commit report):

• lib/errors/classifier.ts - 2.77% coverage
• lib/errors/handler.ts - 8.57% coverage
• lib/errors/utils.ts - 0% coverage
• hooks/useTocSync.ts - 33.33% coverage
• hooks/usePerformanceTracking.ts - 46.15% coverage
• lib/security.ts - 38.77% coverage
• lib/performance/budgets.ts - 54.54% coverage
• lib/performance/metrics.ts - 58.57% coverage
• Various UI components with low coverage

Tasks

Task 1: Fix Flaky TabStatePersistence Test

• Investigate test behavior in isolation vs full suite
• Identify race condition or timing dependency
• Fix test to be deterministic and reliable
• Verify test passes consistently in full suite (run 10+ times)
• Document any test infrastructure improvements

Task 2: Improve Frontend Test Coverage to 85%

• Generate detailed coverage report: npm test -- --coverage
• Prioritize critical files with low coverage (security, errors, performance)
• Write unit tests for:
  • lib/errors/* (classifier, handler, utils)
  • lib/security.ts
  • hooks/useTocSync.ts
  • hooks/usePerformanceTracking.ts
  • lib/performance/* (budgets, metrics)
• Add tests for edge cases in existing components
• Achieve 85%+ coverage across all metrics (statements, branches, lines, functions)
• Verify coverage with: npm test -- --coverage --coverageThreshold='{"global":{"lines":85}}'

Acceptance Criteria

For Flaky Test Fix

• Test passes when run individually
• Test passes consistently in full test suite (10+ consecutive runs)
• No arbitrary timeouts or race conditions remain
• Test execution time < 2s
• Test is properly isolated (no shared state)

For Coverage Improvement

• Overall statement coverage ≥ 85%
• Overall branch coverage ≥ 75%
• Overall line coverage ≥ 85%
• Overall function coverage ≥ 85%
• Pre-commit hooks pass without --no-verify
• All new tests are meaningful (not just coverage padding)

Context

Related PR: #67 - AI service error handling and caching
Related Commit: 75c8278
Beads Issue: auto-author-0fy
Priority: P1 (High) - Blocks clean commits
Type: Bug (technical debt)

Success Metrics

1. ✅ Pre-commit hooks pass completely
2. ✅ No need for --no-verify on future commits
3. ✅ CI/CD pipeline validates coverage automatically
4. ✅ Test suite is reliable and deterministic

Notes

• The AI error handling implementation (PR feat: Implement AI service error handling and caching #67) has 100% test coverage with 77 passing tests
• This issue addresses pre-existing test infrastructure debt
• Fixing this unblocks the TDD workflow for all future development

References

• Pre-commit config: .pre-commit-config.yaml
• Test coverage report: Run npm test -- --coverage in frontend/
• Flaky test file: frontend/src/__tests__/TabStatePersistence.test.tsx
• Coverage config: frontend/jest.config.js

---

Created from beads issue: auto-author-0fy
Beads Priority: P1
Beads Type: bug

🤖 Generated with Claude Code

[traycerai]

Plan

Observations

The flaky test in file:frontend/src/__tests__/TabStatePersistence.test.tsx fails due to a race condition with the debounced auto-save mechanism in useChapterTabs hook (1-second debounce on line 243). When run individually, Jest's timers work correctly, but in a full suite, timer mocking conflicts with other tests cause the debounce to not fire reliably. The coverage gaps are concentrated in critical infrastructure: error handling (classifier, handler, utils), security utilities, performance tracking, and TOC synchronization—all recently added modules with minimal test coverage.

Approach

The plan addresses both issues systematically: First, fix the flaky test by properly managing Jest's fake timers and ensuring test isolation. Second, achieve 85% coverage by writing comprehensive unit tests for the eight low-coverage modules, prioritizing security and error handling (P1), then performance and hooks (P2). Tests will follow existing patterns from file:frontend/src/lib/errors/errorHandler.test.ts and use the established test infrastructure in file:frontend/src/jest.setup.ts. All tests will be meaningful, covering edge cases, error paths, and integration scenarios rather than just padding coverage numbers.

Implementation Steps

Task 1: Fix Flaky TabStatePersistence Test

1.1 Identify Root Cause

• Examine file:frontend/src/__tests__/TabStatePersistence.test.tsx line 114-139
• The test "saves tab state to localStorage and backend on state changes" expects mockLocalStorage.setItem to be called after setActiveChapter
• The auto-save in file:frontend/src/hooks/useChapterTabs.ts lines 241-246 uses a 1-second debounce via setTimeout
• When tests run in parallel, Jest's timer mocking state can leak between tests

1.2 Fix Timer Management

• Add jest.useFakeTimers() at the start of the failing test
• After calling setActiveChapter, use jest.advanceTimersByTime(1000) to trigger the debounced save
• Wrap timer advancement in act() to ensure React state updates complete
• Add jest.useRealTimers() in cleanup to prevent timer leakage

Pattern to apply:

test('saves tab state to localStorage and backend on state changes', async () => {
  jest.useFakeTimers();
  // ... existing setup ...
  
  act(() => {
    result.current.actions.setActiveChapter('ch2');
  });
  
  // Advance timers to trigger debounced save
  act(() => {
    jest.advanceTimersByTime(1000);
  });
  
  await waitFor(() => {
    expect(mockLocalStorage.setItem).toHaveBeenCalled();
  });
  
  jest.useRealTimers();
});

1.3 Ensure Test Isolation

• Add jest.clearAllTimers() to the beforeEach block in file:frontend/src/__tests__/TabStatePersistence.test.tsx
• Verify mockLocalStorage.clear() is called before each test (already present on line 59)
• Add afterEach hook to restore real timers: afterEach(() => { jest.useRealTimers(); })

1.4 Verify Fix

• Run the test individually 10 times: npm test -- TabStatePersistence.test.tsx --testNamePattern="saves tab state"
• Run full test suite 10 times: npm test -- --watchAll=false
• Ensure test execution time remains under 2 seconds
• Check that no other tests are affected by timer changes

---

Task 2: Improve Frontend Test Coverage to 85%

2.1 Create Tests for Error Utilities (Priority: Critical)

File: file:frontend/src/lib/errors/utils.ts (0% coverage)

Create file:frontend/src/lib/errors/__tests__/utils.test.ts:

• Test generateCorrelationId():

  • Generates unique IDs on multiple calls
  • Returns string in format timestamp-random
  • IDs are different across calls

• Test calculateRetryDelay():

  • Returns base delay when exponential backoff disabled
  • Calculates exponential backoff correctly (2^attempt)
  • Respects max delay cap
  • Handles attempt=0 correctly

• Test sleep():

  • Resolves after specified milliseconds
  • Works with fake timers

• Test canRetry():

  • Returns true when attempts < maxAttempts
  • Returns false when attempts >= maxAttempts
  • Handles edge cases (0 attempts, negative values)

• Test formatErrorMessage():

  • Returns message only when no details
  • Combines message and details with newline
  • Handles empty strings

• Test getErrorMessage():

  • Extracts message from Error objects
  • Returns string directly for string errors
  • Extracts message/error from objects
  • Returns default for unknown types

Coverage target: 100%

---

2.2 Expand Error Classifier Tests (Priority: Critical)

File: file:frontend/src/lib/errors/classifier.ts (2.77% coverage)

Create file:frontend/src/lib/errors/__tests__/classifier.test.ts:

• Test classifyError() with API errors:

  • Handles 400 (validation) errors with field errors
  • Handles 401 (unauthorized) errors
  • Handles 403 (forbidden) errors
  • Handles 404 (not found) errors
  • Handles 429 (rate limit) errors
  • Handles 500 (server) errors
  • Handles 502/503 (service unavailable) errors
  • Handles 504 (timeout) errors
  • Extracts status codes from both statusCode and status properties

• Test network error classification:

  • Detects "network" in error message
  • Detects "fetch" in error message
  • Detects "connection" in error message
  • Detects "offline" in error message
  • Sets retryable=true and TRANSIENT type

• Test timeout error classification:

  • Detects "timeout" in error message
  • Detects "timed out" in error message
  • Uses longer retry delays

• Test validation error classification:

  • Identifies 400/422 status codes
  • Extracts field errors from multiple formats
  • Sets retryable=false

• Test field error extraction:

  • Format: { errors: { field: "message" } }
  • Format: { fieldErrors: { field: "message" } }
  • Format: { validationErrors: [{ field, message }] }
  • Returns undefined for non-API errors

• Test user-friendly messages:

  • Uses custom userMessage if provided
  • Falls back to status-specific messages
  • Provides generic messages for unknown codes

• Test suggested actions:

  • Returns appropriate actions for TRANSIENT errors
  • Returns auth-specific actions for 401
  • Returns permission actions for 403
  • Returns navigation actions for 404
  • Returns system actions for unknown errors

Coverage target: 95%+

---

2.3 Expand Error Handler Tests (Priority: Critical)

File: file:frontend/src/lib/errors/handler.ts (8.57% coverage)

Expand file:frontend/src/lib/errors/errorHandler.test.ts:

• Test handleApiCall() success scenarios:

  • Returns success result with data
  • Calls onSuccess callback after retries
  • Tracks attempt count correctly

• Test retry logic:

  • Retries on TRANSIENT errors
  • Does not retry on PERMANENT errors
  • Does not retry on SYSTEM errors
  • Respects maxAttempts limit
  • Calls onRetry callback before each retry
  • Uses exponential backoff delays
  • Respects maxDelay cap

• Test failure scenarios:

  • Calls onFailure callback when exhausted
  • Returns error result with classified error
  • Includes attempt count in result

• Test custom retry configuration:

  • Merges with default config
  • Overrides maxAttempts
  • Overrides delay settings
  • Overrides exponential backoff flag

• Test createRetryWrapper():

  • Creates wrapper function with correct signature
  • Passes arguments through to wrapped function
  • Applies default options
  • Returns ErrorHandlerResult

• Test manualRetry():

  • Calls onRetry callback
  • Uses maxAttempts=1
  • Returns result from handleApiCall

Coverage target: 95%+

---

2.4 Create Security Tests (Priority: Critical)

File: file:frontend/src/lib/security.ts (38.77% coverage)

Create file:frontend/src/lib/__tests__/security.test.ts:

• Test sanitizeHtml():

  • Allows safe tags (p, strong, em, h1-h6, ul, ol, li)
  • Removes script tags
  • Removes dangerous attributes (onclick, onerror, onload)
  • Removes style attributes
  • Respects custom allowedTags option
  • Respects custom allowedAttributes option

• Test sanitizeText():

  • Removes HTML tags
  • Removes dangerous characters (<, >, ", ')
  • Removes javascript: protocol
  • Removes data: protocol
  • Removes vbscript: protocol
  • Trims whitespace
  • Returns empty string for non-string input

• Test sanitizeEmail():

  • Converts to lowercase
  • Trims whitespace
  • Removes invalid characters
  • Validates email format with regex
  • Returns empty string for invalid emails
  • Returns empty string for non-string input

• Test sanitizeUrl():

  • Blocks javascript: protocol
  • Blocks data: protocol
  • Blocks vbscript: protocol
  • Blocks file: protocol
  • Blocks ftp: protocol
  • Allows http:// URLs
  • Allows https:// URLs
  • Allows relative URLs (/)
  • Allows protocol-relative URLs (//)
  • Returns empty string for dangerous URLs
  • Returns empty string for non-string input

• Test sanitizeFileName():

  • Replaces invalid characters with underscore
  • Removes leading dots
  • Removes trailing dots
  • Limits length to 255 characters
  • Returns empty string for non-string input

• Test RateLimiter class:

  • Allows requests within limit
  • Blocks requests exceeding limit
  • Resets after time window
  • Tracks multiple identifiers separately
  • Reset method clears attempts

• Test exported rate limiters:

  • loginRateLimiter has correct config (5 attempts, 15 min)
  • apiRateLimiter has correct config (100 attempts, 1 min)

Coverage target: 95%+

---

2.5 Create TOC Sync Tests (Priority: High)

File: file:frontend/src/hooks/useTocSync.ts (33.33% coverage)

Create file:frontend/src/hooks/__tests__/useTocSync.test.ts:

• Test useTocSync() hook:

  • Initializes with bookId
  • Generates TOC hash from API response
  • Detects TOC changes via hash comparison
  • Calls onTocChanged when hash differs
  • Listens for custom 'tocUpdated' events
  • Filters events by bookId
  • Listens for localStorage 'storage' events
  • Clears localStorage flag after handling
  • Polls for changes when pollInterval > 0
  • Cleans up polling timeout on unmount
  • Cleans up event listeners on unmount

• Test generateTocHash():

  • Creates consistent hash for same TOC structure
  • Creates different hash for different TOC
  • Handles chapters with subchapters
  • Returns null on API error

• Test triggerTocUpdateEvent():

  • Dispatches custom 'tocUpdated' event
  • Sets localStorage flag with timestamp
  • Includes bookId in event detail

• Mock bookClient.getToc for all tests

• Use renderHook from @testing-library/react

• Mock window event listeners

• Use fake timers for polling tests

Coverage target: 90%+

---

2.6 Create Performance Tracking Tests (Priority: High)

File: file:frontend/src/hooks/usePerformanceTracking.ts (46.15% coverage)

Create file:frontend/src/hooks/__tests__/usePerformanceTracking.test.ts:

• Test usePerformanceTracking() hook:

  • Returns trackOperation function
  • Returns trackSync function
  • Returns createTracker function

• Test trackOperation():

  • Executes async operation
  • Returns data and metric
  • Measures duration accurately
  • Checks budget from budgets.ts
  • Sets exceeded_budget flag correctly
  • Logs warning when budget exceeded
  • Handles operation errors
  • Re-throws errors after logging
  • Cleans up tracker on completion
  • Cleans up tracker on error

• Test trackSync():

  • Executes sync operation
  • Returns data and metric
  • Measures duration accurately
  • Checks budget
  • Logs warning when budget exceeded
  • Handles operation errors

• Test createTracker():

  • Returns tracker object with end() method
  • Returns tracker object with cancel() method
  • end() returns metric
  • end() accepts additional metadata
  • cancel() prevents reporting
  • Cleans up on end()
  • Cleans up on cancel()

• Mock getBudget from file:frontend/src/lib/performance/budgets.ts

• Mock PerformanceTracker from file:frontend/src/lib/performance/metrics.ts

• Use renderHook from @testing-library/react

Coverage target: 90%+

---

2.7 Expand Performance Budgets Tests (Priority: Medium)

File: file:frontend/src/lib/performance/budgets.ts (54.54% coverage)

Create file:frontend/src/lib/performance/__tests__/budgets.test.ts:

• Test getBudget():

  • Returns budget for known operation
  • Returns undefined for unknown operation
  • Returns correct budget structure

• Test getBudgetsByPriority():

  • Returns all priority 1 budgets
  • Returns all priority 2 budgets
  • Returns all priority 3 budgets
  • Returns empty array for invalid priority

• Test checkBudget():

  • Returns exceeded=true when duration > budget
  • Returns exceeded=false when duration <= budget
  • Calculates overrun correctly
  • Calculates percentage correctly
  • Sets shouldWarn based on warningThreshold
  • Returns null budget for unknown operation

• Test getBudgetStatus():

  • Returns exceeded message with emoji
  • Returns warning message when near limit
  • Returns success message when within budget
  • Returns no-budget message for unknown operation

• Test getCriticalOperations():

  • Returns only priority 1 operations
  • Includes expected critical operations

• Test generateBudgetReport():

  • Returns all budgets
  • Sorts by priority first
  • Sorts by target time within priority

• Verify PERFORMANCE_BUDGETS structure:

  • All budgets have required fields
  • All budgets have valid priority (1, 2, or 3)
  • All budgets have positive target values

Coverage target: 95%+

---

2.8 Expand Performance Metrics Tests (Priority: Medium)

File: file:frontend/src/lib/performance/metrics.ts (58.57% coverage)

Create file:frontend/src/lib/performance/__tests__/metrics.test.ts:

• Test PerformanceTracker class:

  • Constructor initializes with name and budget
  • Constructor captures start time
  • end() calculates duration correctly
  • end() sets exceeded_budget flag
  • end() rates operation based on budget
  • end() includes metadata
  • end() merges additional metadata
  • cancel() prevents reporting

• Test initializeWebVitals():

  • Registers CLS callback
  • Registers INP callback
  • Registers LCP callback
  • Registers TTFB callback
  • Registers FCP callback
  • Callbacks send to analytics

• Test getCachedMetrics():

  • Returns cached metrics from localStorage
  • Returns empty array when no cache
  • Handles JSON parse errors

• Test clearCachedMetrics():

  • Removes metrics from localStorage
  • Handles errors gracefully

• Test rating functions:

  • rateWebVital() rates LCP correctly (good < 2500, poor > 4000)
  • rateWebVital() rates INP correctly (good < 200, poor > 500)
  • rateWebVital() rates CLS correctly (good < 0.1, poor > 0.25)
  • rateWebVital() rates TTFB correctly (good < 800, poor > 1800)
  • rateWebVital() rates FCP correctly (good < 1800, poor > 3000)
  • rateOperation() rates based on budget ratio

• Test sendToAnalytics():

  • Logs to console in development
  • Stores in localStorage in production
  • Limits cache to 100 metrics
  • Handles storage errors

• Mock web-vitals callbacks (already mocked in file:frontend/src/jest.setup.ts)

• Mock localStorage

• Mock performance.now()

Coverage target: 90%+

---

Task 3: Verification and Validation

3.1 Run Coverage Report

• Execute: cd frontend && npm test -- --coverage --watchAll=false
• Verify all target files meet coverage thresholds:
  • Statements: ≥ 85%
  • Branches: ≥ 75%
  • Lines: ≥ 85%
  • Functions: ≥ 85%

3.2 Run Pre-commit Hooks

• Execute: pre-commit run --all-files
• Verify all hooks pass:
  • frontend-lint
  • frontend-typecheck
  • frontend-unit-tests
  • frontend-coverage
  • frontend-e2e-tests

3.3 Validate Test Quality

• Review each test file for:
  • Meaningful assertions (not just coverage padding)
  • Edge case coverage
  • Error path testing
  • Integration scenarios
  • Clear test descriptions
  • Proper setup/teardown

3.4 Run Full Test Suite Multiple Times

• Execute: npm test -- --watchAll=false 10 times
• Verify TabStatePersistence test passes consistently
• Verify no new flaky tests introduced
• Verify total test execution time is reasonable

---

Test File Structure

All new test files should follow this structure:

describe('ModuleName', () => {
  beforeEach(() => {
    // Setup mocks and reset state
  });

  afterEach(() => {
    // Cleanup
    jest.clearAllMocks();
  });

  describe('functionName', () => {
    it('should handle normal case', () => {
      // Arrange
      // Act
      // Assert
    });

    it('should handle edge case', () => {
      // Test edge cases
    });

    it('should handle error case', () => {
      // Test error paths
    });
  });
});

---

Success Criteria

Flaky Test Fix

• ✅ TabStatePersistence test passes individually
• ✅ TabStatePersistence test passes in full suite (10+ consecutive runs)
• ✅ Test execution time < 2 seconds
• ✅ No timer leakage affecting other tests

Coverage Improvement

• ✅ Overall statement coverage ≥ 85%
• ✅ Overall branch coverage ≥ 75%
• ✅ Overall line coverage ≥ 85%
• ✅ Overall function coverage ≥ 85%
• ✅ All 8 low-coverage files improved significantly
• ✅ Pre-commit hooks pass without --no-verify

Test Quality

• ✅ All tests are meaningful and test real behavior
• ✅ Edge cases and error paths covered
• ✅ Tests follow existing patterns and conventions
• ✅ No arbitrary timeouts or race conditions
• ✅ Proper test isolation and cleanup

---

Test Execution Summary

Module	Current Coverage	Target Coverage	Test File
lib/errors/utils.ts	0%	100%	lib/errors/__tests__/utils.test.ts
lib/errors/classifier.ts	2.77%	95%+	lib/errors/__tests__/classifier.test.ts
lib/errors/handler.ts	8.57%	95%+	Expand lib/errors/errorHandler.test.ts
lib/security.ts	38.77%	95%+	lib/__tests__/security.test.ts
hooks/useTocSync.ts	33.33%	90%+	hooks/__tests__/useTocSync.test.ts
hooks/usePerformanceTracking.ts	46.15%	90%+	hooks/__tests__/usePerformanceTracking.test.ts
lib/performance/budgets.ts	54.54%	95%+	lib/performance/__tests__/budgets.test.ts
lib/performance/metrics.ts	58.57%	90%+	lib/performance/__tests__/metrics.test.ts

---

Implementation Flow

graph TD
    A[Start] --> B[Fix Flaky Test]
    B --> C[Add Timer Management]
    C --> D[Ensure Test Isolation]
    D --> E[Verify Fix 10x]
    E --> F{Test Passes?}
    F -->|No| C
    F -->|Yes| G[Create Error Utils Tests]
    G --> H[Create Error Classifier Tests]
    H --> I[Expand Error Handler Tests]
    I --> J[Create Security Tests]
    J --> K[Create TOC Sync Tests]
    K --> L[Create Performance Tracking Tests]
    L --> M[Expand Performance Budgets Tests]
    M --> N[Expand Performance Metrics Tests]
    N --> O[Run Coverage Report]
    O --> P{Coverage ≥ 85%?}
    P -->|No| Q[Identify Gaps]
    Q --> R[Add Missing Tests]
    R --> O
    P -->|Yes| S[Run Pre-commit Hooks]
    S --> T{All Hooks Pass?}
    T -->|No| U[Fix Issues]
    U --> S
    T -->|Yes| V[Validate Test Quality]
    V --> W[Run Full Suite 10x]
    W --> X{All Tests Pass?}
    X -->|No| Y[Debug Failures]
    Y --> W
    X -->|Yes| Z[Complete]

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Import In IDE

🤖 Prompt for AI Agents

## Observations

The flaky test in `file:frontend/src/__tests__/TabStatePersistence.test.tsx` fails due to a race condition with the debounced auto-save mechanism in `useChapterTabs` hook (1-second debounce on line 243). When run individually, Jest's timers work correctly, but in a full suite, timer mocking conflicts with other tests cause the debounce to not fire reliably. The coverage gaps are concentrated in critical infrastructure: error handling (classifier, handler, utils), security utilities, performance tracking, and TOC synchronization—all recently added modules with minimal test coverage.

## Approach

The plan addresses both issues systematically: First, fix the flaky test by properly managing Jest's fake timers and ensuring test isolation. Second, achieve 85% coverage by writing comprehensive unit tests for the eight low-coverage modules, prioritizing security and error handling (P1), then performance and hooks (P2). Tests will follow existing patterns from `file:frontend/src/lib/errors/errorHandler.test.ts` and use the established test infrastructure in `file:frontend/src/jest.setup.ts`. All tests will be meaningful, covering edge cases, error paths, and integration scenarios rather than just padding coverage numbers.

## Implementation Steps

### Task 1: Fix Flaky TabStatePersistence Test

#### 1.1 Identify Root Cause
- Examine `file:frontend/src/__tests__/TabStatePersistence.test.tsx` line 114-139
- The test "saves tab state to localStorage and backend on state changes" expects `mockLocalStorage.setItem` to be called after `setActiveChapter`
- The auto-save in `file:frontend/src/hooks/useChapterTabs.ts` lines 241-246 uses a 1-second debounce via `setTimeout`
- When tests run in parallel, Jest's timer mocking state can leak between tests

#### 1.2 Fix Timer Management
- Add `jest.useFakeTimers()` at the start of the failing test
- After calling `setActiveChapter`, use `jest.advanceTimersByTime(1000)` to trigger the debounced save
- Wrap timer advancement in `act()` to ensure React state updates complete
- Add `jest.useRealTimers()` in cleanup to prevent timer leakage

**Pattern to apply:**
```
test('saves tab state to localStorage and backend on state changes', async () => {
  jest.useFakeTimers();
  // ... existing setup ...
  
  act(() => {
    result.current.actions.setActiveChapter('ch2');
  });
  
  // Advance timers to trigger debounced save
  act(() => {
    jest.advanceTimersByTime(1000);
  });
  
  await waitFor(() => {
    expect(mockLocalStorage.setItem).toHaveBeenCalled();
  });
  
  jest.useRealTimers();
});
```

#### 1.3 Ensure Test Isolation
- Add `jest.clearAllTimers()` to the `beforeEach` block in `file:frontend/src/__tests__/TabStatePersistence.test.tsx`
- Verify `mockLocalStorage.clear()` is called before each test (already present on line 59)
- Add `afterEach` hook to restore real timers: `afterEach(() => { jest.useRealTimers(); })`

#### 1.4 Verify Fix
- Run the test individually 10 times: `npm test -- TabStatePersistence.test.tsx --testNamePattern="saves tab state"`
- Run full test suite 10 times: `npm test -- --watchAll=false`
- Ensure test execution time remains under 2 seconds
- Check that no other tests are affected by timer changes

---

### Task 2: Improve Frontend Test Coverage to 85%

#### 2.1 Create Tests for Error Utilities (Priority: Critical)

**File: `file:frontend/src/lib/errors/utils.ts` (0% coverage)**

Create `file:frontend/src/lib/errors/__tests__/utils.test.ts`:

- Test `generateCorrelationId()`:
  - Generates unique IDs on multiple calls
  - Returns string in format `timestamp-random`
  - IDs are different across calls

- Test `calculateRetryDelay()`:
  - Returns base delay when exponential backoff disabled
  - Calculates exponential backoff correctly (2^attempt)
  - Respects max delay cap
  - Handles attempt=0 correctly

- Test `sleep()`:
  - Resolves after specified milliseconds
  - Works with fake timers

- Test `canRetry()`:
  - Returns true when attempts < maxAttempts
  - Returns false when attempts >= maxAttempts
  - Handles edge cases (0 attempts, negative values)

- Test `formatErrorMessage()`:
  - Returns message only when no details
  - Combines message and details with newline
  - Handles empty strings

- Test `getErrorMessage()`:
  - Extracts message from Error objects
  - Returns string directly for string errors
  - Extracts message/error from objects
  - Returns default for unknown types

**Coverage target: 100%**

---

#### 2.2 Expand Error Classifier Tests (Priority: Critical)

**File: `file:frontend/src/lib/errors/classifier.ts` (2.77% coverage)**

Create `file:frontend/src/lib/errors/__tests__/classifier.test.ts`:

- Test `classifyError()` with API errors:
  - Handles 400 (validation) errors with field errors
  - Handles 401 (unauthorized) errors
  - Handles 403 (forbidden) errors
  - Handles 404 (not found) errors
  - Handles 429 (rate limit) errors
  - Handles 500 (server) errors
  - Handles 502/503 (service unavailable) errors
  - Handles 504 (timeout) errors
  - Extracts status codes from both `statusCode` and `status` properties

- Test network error classification:
  - Detects "network" in error message
  - Detects "fetch" in error message
  - Detects "connection" in error message
  - Detects "offline" in error message
  - Sets retryable=true and TRANSIENT type

- Test timeout error classification:
  - Detects "timeout" in error message
  - Detects "timed out" in error message
  - Uses longer retry delays

- Test validation error classification:
  - Identifies 400/422 status codes
  - Extracts field errors from multiple formats
  - Sets retryable=false

- Test field error extraction:
  - Format: `{ errors: { field: "message" } }`
  - Format: `{ fieldErrors: { field: "message" } }`
  - Format: `{ validationErrors: [{ field, message }] }`
  - Returns undefined for non-API errors

- Test user-friendly messages:
  - Uses custom `userMessage` if provided
  - Falls back to status-specific messages
  - Provides generic messages for unknown codes

- Test suggested actions:
  - Returns appropriate actions for TRANSIENT errors
  - Returns auth-specific actions for 401
  - Returns permission actions for 403
  - Returns navigation actions for 404
  - Returns system actions for unknown errors

**Coverage target: 95%+**

---

#### 2.3 Expand Error Handler Tests (Priority: Critical)

**File: `file:frontend/src/lib/errors/handler.ts` (8.57% coverage)**

Expand `file:frontend/src/lib/errors/errorHandler.test.ts`:

- Test `handleApiCall()` success scenarios:
  - Returns success result with data
  - Calls onSuccess callback after retries
  - Tracks attempt count correctly

- Test retry logic:
  - Retries on TRANSIENT errors
  - Does not retry on PERMANENT errors
  - Does not retry on SYSTEM errors
  - Respects maxAttempts limit
  - Calls onRetry callback before each retry
  - Uses exponential backoff delays
  - Respects maxDelay cap

- Test failure scenarios:
  - Calls onFailure callback when exhausted
  - Returns error result with classified error
  - Includes attempt count in result

- Test custom retry configuration:
  - Merges with default config
  - Overrides maxAttempts
  - Overrides delay settings
  - Overrides exponential backoff flag

- Test `createRetryWrapper()`:
  - Creates wrapper function with correct signature
  - Passes arguments through to wrapped function
  - Applies default options
  - Returns ErrorHandlerResult

- Test `manualRetry()`:
  - Calls onRetry callback
  - Uses maxAttempts=1
  - Returns result from handleApiCall

**Coverage target: 95%+**

---

#### 2.4 Create Security Tests (Priority: Critical)

**File: `file:frontend/src/lib/security.ts` (38.77% coverage)**

Create `file:frontend/src/lib/__tests__/security.test.ts`:

- Test `sanitizeHtml()`:
  - Allows safe tags (p, strong, em, h1-h6, ul, ol, li)
  - Removes script tags
  - Removes dangerous attributes (onclick, onerror, onload)
  - Removes style attributes
  - Respects custom allowedTags option
  - Respects custom allowedAttributes option

- Test `sanitizeText()`:
  - Removes HTML tags
  - Removes dangerous characters (<, >, ", ')
  - Removes javascript: protocol
  - Removes data: protocol
  - Removes vbscript: protocol
  - Trims whitespace
  - Returns empty string for non-string input

- Test `sanitizeEmail()`:
  - Converts to lowercase
  - Trims whitespace
  - Removes invalid characters
  - Validates email format with regex
  - Returns empty string for invalid emails
  - Returns empty string for non-string input

- Test `sanitizeUrl()`:
  - Blocks javascript: protocol
  - Blocks data: protocol
  - Blocks vbscript: protocol
  - Blocks file: protocol
  - Blocks ftp: protocol
  - Allows http:// URLs
  - Allows https:// URLs
  - Allows relative URLs (/)
  - Allows protocol-relative URLs (//)
  - Returns empty string for dangerous URLs
  - Returns empty string for non-string input

- Test `sanitizeFileName()`:
  - Replaces invalid characters with underscore
  - Removes leading dots
  - Removes trailing dots
  - Limits length to 255 characters
  - Returns empty string for non-string input

- Test `RateLimiter` class:
  - Allows requests within limit
  - Blocks requests exceeding limit
  - Resets after time window
  - Tracks multiple identifiers separately
  - Reset method clears attempts

- Test exported rate limiters:
  - `loginRateLimiter` has correct config (5 attempts, 15 min)
  - `apiRateLimiter` has correct config (100 attempts, 1 min)

**Coverage target: 95%+**

---

#### 2.5 Create TOC Sync Tests (Priority: High)

**File: `file:frontend/src/hooks/useTocSync.ts` (33.33% coverage)**

Create `file:frontend/src/hooks/__tests__/useTocSync.test.ts`:

- Test `useTocSync()` hook:
  - Initializes with bookId
  - Generates TOC hash from API response
  - Detects TOC changes via hash comparison
  - Calls onTocChanged when hash differs
  - Listens for custom 'tocUpdated' events
  - Filters events by bookId
  - Listens for localStorage 'storage' events
  - Clears localStorage flag after handling
  - Polls for changes when pollInterval > 0
  - Cleans up polling timeout on unmount
  - Cleans up event listeners on unmount

- Test `generateTocHash()`:
  - Creates consistent hash for same TOC structure
  - Creates different hash for different TOC
  - Handles chapters with subchapters
  - Returns null on API error

- Test `triggerTocUpdateEvent()`:
  - Dispatches custom 'tocUpdated' event
  - Sets localStorage flag with timestamp
  - Includes bookId in event detail

- Mock `bookClient.getToc` for all tests
- Use `renderHook` from `@testing-library/react`
- Mock window event listeners
- Use fake timers for polling tests

**Coverage target: 90%+**

---

#### 2.6 Create Performance Tracking Tests (Priority: High)

**File: `file:frontend/src/hooks/usePerformanceTracking.ts` (46.15% coverage)**

Create `file:frontend/src/hooks/__tests__/usePerformanceTracking.test.ts`:

- Test `usePerformanceTracking()` hook:
  - Returns trackOperation function
  - Returns trackSync function
  - Returns createTracker function

- Test `trackOperation()`:
  - Executes async operation
  - Returns data and metric
  - Measures duration accurately
  - Checks budget from budgets.ts
  - Sets exceeded_budget flag correctly
  - Logs warning when budget exceeded
  - Handles operation errors
  - Re-throws errors after logging
  - Cleans up tracker on completion
  - Cleans up tracker on error

- Test `trackSync()`:
  - Executes sync operation
  - Returns data and metric
  - Measures duration accurately
  - Checks budget
  - Logs warning when budget exceeded
  - Handles operation errors

- Test `createTracker()`:
  - Returns tracker object with end() method
  - Returns tracker object with cancel() method
  - end() returns metric
  - end() accepts additional metadata
  - cancel() prevents reporting
  - Cleans up on end()
  - Cleans up on cancel()

- Mock `getBudget` from `file:frontend/src/lib/performance/budgets.ts`
- Mock `PerformanceTracker` from `file:frontend/src/lib/performance/metrics.ts`
- Use `renderHook` from `@testing-library/react`

**Coverage target: 90%+**

---

#### 2.7 Expand Performance Budgets Tests (Priority: Medium)

**File: `file:frontend/src/lib/performance/budgets.ts` (54.54% coverage)**

Create `file:frontend/src/lib/performance/__tests__/budgets.test.ts`:

- Test `getBudget()`:
  - Returns budget for known operation
  - Returns undefined for unknown operation
  - Returns correct budget structure

- Test `getBudgetsByPriority()`:
  - Returns all priority 1 budgets
  - Returns all priority 2 budgets
  - Returns all priority 3 budgets
  - Returns empty array for invalid priority

- Test `checkBudget()`:
  - Returns exceeded=true when duration > budget
  - Returns exceeded=false when duration <= budget
  - Calculates overrun correctly
  - Calculates percentage correctly
  - Sets shouldWarn based on warningThreshold
  - Returns null budget for unknown operation

- Test `getBudgetStatus()`:
  - Returns exceeded message with emoji
  - Returns warning message when near limit
  - Returns success message when within budget
  - Returns no-budget message for unknown operation

- Test `getCriticalOperations()`:
  - Returns only priority 1 operations
  - Includes expected critical operations

- Test `generateBudgetReport()`:
  - Returns all budgets
  - Sorts by priority first
  - Sorts by target time within priority

- Verify `PERFORMANCE_BUDGETS` structure:
  - All budgets have required fields
  - All budgets have valid priority (1, 2, or 3)
  - All budgets have positive target values

**Coverage target: 95%+**

---

#### 2.8 Expand Performance Metrics Tests (Priority: Medium)

**File: `file:frontend/src/lib/performance/metrics.ts` (58.57% coverage)**

Create `file:frontend/src/lib/performance/__tests__/metrics.test.ts`:

- Test `PerformanceTracker` class:
  - Constructor initializes with name and budget
  - Constructor captures start time
  - end() calculates duration correctly
  - end() sets exceeded_budget flag
  - end() rates operation based on budget
  - end() includes metadata
  - end() merges additional metadata
  - cancel() prevents reporting

- Test `initializeWebVitals()`:
  - Registers CLS callback
  - Registers INP callback
  - Registers LCP callback
  - Registers TTFB callback
  - Registers FCP callback
  - Callbacks send to analytics

- Test `getCachedMetrics()`:
  - Returns cached metrics from localStorage
  - Returns empty array when no cache
  - Handles JSON parse errors

- Test `clearCachedMetrics()`:
  - Removes metrics from localStorage
  - Handles errors gracefully

- Test rating functions:
  - `rateWebVital()` rates LCP correctly (good < 2500, poor > 4000)
  - `rateWebVital()` rates INP correctly (good < 200, poor > 500)
  - `rateWebVital()` rates CLS correctly (good < 0.1, poor > 0.25)
  - `rateWebVital()` rates TTFB correctly (good < 800, poor > 1800)
  - `rateWebVital()` rates FCP correctly (good < 1800, poor > 3000)
  - `rateOperation()` rates based on budget ratio

- Test `sendToAnalytics()`:
  - Logs to console in development
  - Stores in localStorage in production
  - Limits cache to 100 metrics
  - Handles storage errors

- Mock `web-vitals` callbacks (already mocked in `file:frontend/src/jest.setup.ts`)
- Mock localStorage
- Mock `performance.now()`

**Coverage target: 90%+**

---

### Task 3: Verification and Validation

#### 3.1 Run Coverage Report
- Execute: `cd frontend && npm test -- --coverage --watchAll=false`
- Verify all target files meet coverage thresholds:
  - Statements: ≥ 85%
  - Branches: ≥ 75%
  - Lines: ≥ 85%
  - Functions: ≥ 85%

#### 3.2 Run Pre-commit Hooks
- Execute: `pre-commit run --all-files`
- Verify all hooks pass:
  - `frontend-lint`
  - `frontend-typecheck`
  - `frontend-unit-tests`
  - `frontend-coverage`
  - `frontend-e2e-tests`

#### 3.3 Validate Test Quality
- Review each test file for:
  - Meaningful assertions (not just coverage padding)
  - Edge case coverage
  - Error path testing
  - Integration scenarios
  - Clear test descriptions
  - Proper setup/teardown

#### 3.4 Run Full Test Suite Multiple Times
- Execute: `npm test -- --watchAll=false` 10 times
- Verify TabStatePersistence test passes consistently
- Verify no new flaky tests introduced
- Verify total test execution time is reasonable

---

## Test File Structure

All new test files should follow this structure:

```
describe('ModuleName', () => {
  beforeEach(() => {
    // Setup mocks and reset state
  });

  afterEach(() => {
    // Cleanup
    jest.clearAllMocks();
  });

  describe('functionName', () => {
    it('should handle normal case', () => {
      // Arrange
      // Act
      // Assert
    });

    it('should handle edge case', () => {
      // Test edge cases
    });

    it('should handle error case', () => {
      // Test error paths
    });
  });
});
```

---

## Success Criteria

### Flaky Test Fix
- ✅ TabStatePersistence test passes individually
- ✅ TabStatePersistence test passes in full suite (10+ consecutive runs)
- ✅ Test execution time < 2 seconds
- ✅ No timer leakage affecting other tests

### Coverage Improvement
- ✅ Overall statement coverage ≥ 85%
- ✅ Overall branch coverage ≥ 75%
- ✅ Overall line coverage ≥ 85%
- ✅ Overall function coverage ≥ 85%
- ✅ All 8 low-coverage files improved significantly
- ✅ Pre-commit hooks pass without `--no-verify`

### Test Quality
- ✅ All tests are meaningful and test real behavior
- ✅ Edge cases and error paths covered
- ✅ Tests follow existing patterns and conventions
- ✅ No arbitrary timeouts or race conditions
- ✅ Proper test isolation and cleanup

---

## Test Execution Summary

| Module | Current Coverage | Target Coverage | Test File |
|--------|-----------------|-----------------|-----------|
| `lib/errors/utils.ts` | 0% | 100% | `lib/errors/__tests__/utils.test.ts` |
| `lib/errors/classifier.ts` | 2.77% | 95%+ | `lib/errors/__tests__/classifier.test.ts` |
| `lib/errors/handler.ts` | 8.57% | 95%+ | Expand `lib/errors/errorHandler.test.ts` |
| `lib/security.ts` | 38.77% | 95%+ | `lib/__tests__/security.test.ts` |
| `hooks/useTocSync.ts` | 33.33% | 90%+ | `hooks/__tests__/useTocSync.test.ts` |
| `hooks/usePerformanceTracking.ts` | 46.15% | 90%+ | `hooks/__tests__/usePerformanceTracking.test.ts` |
| `lib/performance/budgets.ts` | 54.54% | 95%+ | `lib/performance/__tests__/budgets.test.ts` |
| `lib/performance/metrics.ts` | 58.57% | 90%+ | `lib/performance/__tests__/metrics.test.ts` |

---

## Implementation Flow

```mermaid
graph TD
    A[Start] --> B[Fix Flaky Test]
    B --> C[Add Timer Management]
    C --> D[Ensure Test Isolation]
    D --> E[Verify Fix 10x]
    E --> F{Test Passes?}
    F -->|No| C
    F -->|Yes| G[Create Error Utils Tests]
    G --> H[Create Error Classifier Tests]
    H --> I[Expand Error Handler Tests]
    I --> J[Create Security Tests]
    J --> K[Create TOC Sync Tests]
    K --> L[Create Performance Tracking Tests]
    L --> M[Expand Performance Budgets Tests]
    M --> N[Expand Performance Metrics Tests]
    N --> O[Run Coverage Report]
    O --> P{Coverage ≥ 85%?}
    P -->|No| Q[Identify Gaps]
    Q --> R[Add Missing Tests]
    R --> O
    P -->|Yes| S[Run Pre-commit Hooks]
    S --> T{All Hooks Pass?}
    T -->|No| U[Fix Issues]
    U --> S
    T -->|Yes| V[Validate Test Quality]
    V --> W[Run Full Suite 10x]
    W --> X{All Tests Pass?}
    X -->|No| Y[Debug Failures]
    Y --> W
    X -->|Yes| Z[Complete]
```

---

Execution Information

Branch: main
Commit: 5300c9d

---

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🔗 Similar Issues

Related Issues

• Replace mocked tab implementation in ChapterQuestions component with functional tabs #43
• Implement robust error handling and fallback for AI service failures #41
• Fix TOC generation flow - ensure reliable generation with proper error handling #48

🔗 Related PRs

#9 - feat: Complete E2E Test Infrastructure with Auth Bypass [merged]
frankbria/codeframe#38 - fix(e2e): Improve Playwright test pass rate from 18% to 57% [merged]
frankbria/codeframe#51 - feat: Add TaskStats component to Dashboard Overview tab [merged]
frankbria/codeframe#75 - test: Add comprehensive test coverage for quality gates components [merged]
frankbria/codeframe#93 - fix(e2e): Fix dashboard and metrics tests for tab-based UI rendering [merged]

👤 Suggested Assignees

• frankbria

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