Increase test coverage for undertested modules

[vladiant]

Summary

Adds 48 new tests targeting four modules that previously had low coverage: PostgresImageRepository (23%), ListImagesUseCase (64%), PillowImageProcessor sync workers (67%), and main.py lifespan (69%). All four modules now reach 100% coverage. Overall test count goes from 168 to 216.

Changes

Added

• test_postgres_image_repository.py (28 tests)
  SQLite-backed integration tests for PostgresImageRepository. Exercises all 8 repository methods (save, get_by_id, list_images, delete, get_expired, delete_expired_batch, count) with real SQL queries and ORM mapping round-trips, using aiosqlite (already a dev dependency). PostgreSQL-specific column types (UUID, ARRAY) are swapped to SQLite equivalents at fixture time.

• test_list_images.py (5 tests)
  Unit tests for ListImagesUseCase covering empty results, response mapping (metadata/thumbnail), pagination parameter forwarding, status filter forwarding, and total-vs-page-size distinction.

• test_pillow_processor.py (12 new tests)
  Direct in-process tests for _generate_thumbnail_sync (aspect ratio, RGBA, small images, JPEG format, corrupt data) and _extract_metadata_sync (RGB/RGBA/grayscale, corrupt data), plus shutdown_executor lifecycle tests. These functions previously ran only in ProcessPoolExecutor child processes invisible to the coverage collector.

• test_lifespan.py (3 tests)
  Integration tests for the FastAPI lifespan async context manager: startup table creation, shutdown cleanup (engine.dispose, shutdown_executor), and log message verification.

Fixed

• Replaced deprecated HTTP_422_UNPROCESSABLE_ENTITY with HTTP_422_UNPROCESSABLE_CONTENT in the upload validation error response.

Coverage impact

Module	Before	After
postgres_image_repository.py	23%	100%
list_images.py	64%	100%
pillow_processor.py	67%	100%
main.py	69%	100%
Overall	—	96%

Version

PATCH bump: 2.0.1 → 2.0.2

Checklist

• ruff check — no issues
• mypy src/ — no issues
• pytest — 216 passed
• CHANGELOG.md updated
• Version bumped in pyproject.toml
• No source logic changes (tests only + deprecation fix)