feat: add comprehensive backend test coverage with proper mocking

[Copilot]

Summary

This PR adds comprehensive test coverage for the backend API, addressing the lack of testing infrastructure identified in the repository. The implementation includes 55 tests covering all major backend components with proper mocking to avoid external dependencies.

What's Added

Configuration Module (4 tests)

• Settings defaults and environment variable loading
• Custom deployment names and optional configurations

Ingestion Pipeline (13 tests)

• Document chunking with tiktoken mocking to avoid network calls
• PDF content extraction with Azure Document Intelligence mocking
• HTML content parsing and cleaning with BeautifulSoup
• Error handling for extraction failures

API Endpoints (8 tests)

• Basic health checks and metadata endpoints
• File upload processing with proper async mocking
• Index statistics with Azure Search client mocking
• Error handling and fallback responses

Chat API (9 tests)

• Streaming chat responses with Server-Sent Events format validation
• Multiple conversation modes (context-aware generation, QA verification)
• Error handling during plan creation and execution
• Request validation and response formatting

Agent Tools (8 tests)

• Azure Search integration with semantic search capabilities
• Document retrieval and relevance scoring logic
• Error handling for connection failures
• Kernel function metadata validation

Agent Workflows (13 tests)

• Orchestrator plan creation for different workflow modes
• Retriever search functionality with proper result mocking
• Writer streaming text generation with OpenAI client mocking
• Verifier confidence scoring and source validation
• Curator document processing pipeline with dependency mocking

Technical Approach

• Comprehensive Mocking: All external dependencies (Azure services, OpenAI, tiktoken) are properly mocked to ensure tests run without network access
• Async Testing: Full support for async/await patterns using pytest-asyncio
• Error Handling: Tests cover both success and failure scenarios for robust validation
• Real Implementation Testing: Tests validate actual business logic rather than just mocking everything

Testing Strategy

All tests use the FastAPI TestClient and proper async mocking patterns. External services like Azure Search, Document Intelligence, and OpenAI are mocked to avoid API calls while still validating the integration logic and error handling.

Example test pattern:

@patch('azure.search.documents.SearchClient')
def test_index_stats_with_mock(mock_search_client):
    mock_client_instance = Mock()
    mock_search_client.return_value = mock_client_instance
    # ... setup mock responses
    
    response = client.get("/api/index-stats")
    assert response.status_code == 200

Results

• ✅ 55 tests with 100% pass rate
• ✅ Coverage for all major backend modules
• ✅ Proper mocking prevents external dependencies
• ✅ Both success and error scenarios tested
• ✅ Async patterns properly validated

Fixes #5.

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

• openaipublic.blob.core.windows.net
  • Triggering command: python -m pytest tests/test_ingestion.py -v (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

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