ComprehendServiceTest:
  ✓ Constructor with default region
  ✓ Constructor with custom region
  ✓ detectPiiEntities returns structured response
  ✓ detectPiiEntities returns false with invalid credentials
  ✓ detectPiiEntities includes error details on failure
  ✓ detectPiiEntities handles empty text
  ✓ detectPiiEntities handles long text (5000 words)
  ✓ detectPiiEntities accepts non-English language code