Add comprehensive test suite for image processing and related services

- Implement tests for database generator to ensure proper session handling.
- Create tests for EXIF extraction and conversion functions.
- Add tests for image-related endpoints, ensuring proper data retrieval and isolation between clients.
- Develop tests for OCR functionality, including language detection and text extraction.
- Introduce tests for the image processing pipeline, covering success and failure scenarios.
- Validate rate limiting functionality and ensure independent counters for different clients.
- Implement scraper tests to verify HTML content fetching and error handling.
- Add unit tests for various services, including storage and filename generation.
- Establish worker entry point for ARQ to handle background image processing tasks.

tests/test_db_generator.py

@@ -0,0 +1,54 @@
+import pytest
+from app.database import get_db
+from unittest.mock import patch, MagicMock
+
+@pytest.mark.asyncio
+async def test_get_db_generator():
+    mock_session = MagicMock()
+    mock_session.commit = AsyncMock()
+    mock_session.rollback = AsyncMock()
+    mock_session.close = AsyncMock()
+    
+    # We need to mock AsyncSessionLocal as context manager
+    mock_session_factory = MagicMock()
+    mock_session_factory.return_value.__aenter__.return_value = mock_session
+    
+    with patch("app.database.AsyncSessionLocal", mock_session_factory):
+        generator = get_db()
+        # Initial yield
+        session = await generator.__anext__()
+        assert session == mock_session
+        
+        # After yield, it tries to commit
+        try:
+            await generator.__anext__()
+        except StopAsyncIteration:
+            pass
+        
+        mock_session.commit.assert_called_once()
+        mock_session.close.assert_called_once()
+
+@pytest.mark.asyncio
+async def test_get_db_generator_exception():
+    mock_session = MagicMock()
+    mock_session.commit = AsyncMock()
+    mock_session.rollback = AsyncMock()
+    mock_session.close = AsyncMock()
+    
+    mock_session_factory = MagicMock()
+    mock_session_factory.return_value.__aenter__.return_value = mock_session
+    
+    with patch("app.database.AsyncSessionLocal", mock_session_factory):
+        generator = get_db()
+        session = await generator.__anext__()
+        
+        # Simulate exception during use
+        with pytest.raises(ValueError):
+            await generator.athrow(ValueError("test error"))
+        
+        mock_session.rollback.assert_called_once()
+        mock_session.close.assert_called_once()
+
+class AsyncMock(MagicMock):
+    async def __call__(self, *args, **kwargs):
+        return super(AsyncMock, self).__call__(*args, **kwargs)