### Testing FolderNamingService

FolderNamingService fixes missing years in anime folder names after NFO refresh. Test file: `tests/unit/test_folder_naming_service.py`.

Key methods tested:
- `_build_target_folder()` — constructs safe "Title (YYYY)" names, strips existing year suffix first (prevents double-year like "Naruto (1999) (1999)")
- `_folder_has_year()` — detects existing `(YYYY)` pattern
- `_extract_year_from_folder_name()` — parses `(YYYY)` suffix
- `_extract_title_from_folder_name()` — strips year suffix

```python
# Safe: repeated calls never accumulate years
r1 = FolderNamingService._build_target_folder("Naruto", 1999)
r2 = FolderNamingService._build_target_folder(r1, 1999)
assert r1 == r2 == "Naruto (1999)"

# Safe: existing year is replaced, not appended
result = FolderNamingService._build_target_folder("Naruto (2020)", 1999)
assert result == "Naruto (1999)"
assert "2020" not in result
```

The service is also tested end-to-end with mocked filesystem and database:
- Renames folder and updates DB when year is missing from folder name
- Skips rename when folder already has a year
- Skips rename when DB has no year
- Skips when target folder already exists on disk
- Safety guard detects and skips if target folder year mismatches DB year

### Mocking aiohttp Sessions

When testing code that uses `aiohttp.ClientSession`:

```python
from unittest.mock import AsyncMock, MagicMock, patch
from aiohttp import ClientSession

# Mock aiohttp session for testing
class MockAiohttpSession:
    def __init__(self):
        self.closed = False
    
    async def close(self):
        self.closed = True
    
    def get(self, url, **kwargs):
        mock_response = AsyncMock()
        mock_response.status = 200
        mock_response.json = AsyncMock(return_value={"data": "test"})
        mock_response.__aenter__ = AsyncMock(return_value=mock_response)
        mock_response.__aexit__ = AsyncMock(return_value=None)
        return mock_response

# Use in fixture
@pytest.fixture
async def mock_tmdb_session():
    session = MockAiohttpSession()
    yield session
    # Cleanup verification
    assert session.closed, "Session was not closed"
```

**Key points:**
- Always verify `session.closed` is `True` after context manager exits
- Mock `__aenter__` and `__aexit__` for response context managers
- Set `closed = False` on mock session for unclosed warning tests

7. Coverage Requirements
8. CI/CD Integration
9. Writing Good Tests
    - Arrange-Act-Assert pattern
    - Test isolation
    - Edge cases
10. Common Pitfalls to Avoid