test: add unit test suite for backend API endpoints (#63)

[SandeepChauhan00]

Summary

Adds the first unit test suite for the backend API, covering all existing endpoints with 28 tests. This establishes the testing foundation for the project.

Closes #63

What's Added

• backend/tests/__init__.py — test package marker
• backend/tests/conftest.py — shared fixtures with mocked heavy dependencies (torch, vertexai, google-cloud, sentence-transformers) so tests run fast without GPU or cloud credentials
• backend/tests/test_health.py — 15 tests covering /, /health, and /api/health
• backend/tests/test_query.py — 13 tests covering /api/chat, /api/session/reset, and unknown routes
• Updated pyproject.toml with [tool.pytest.ini_options] configuration

Test Results

All 28 tests pass on Python 3.14:

backend/tests/test_health.py::TestRootEndpoint::test_root_returns_200 PASSED
backend/tests/test_health.py::TestRootEndpoint::test_root_contains_message PASSED
backend/tests/test_health.py::TestRootEndpoint::test_root_contains_version PASSED
backend/tests/test_health.py::TestHealthEndpoint::test_health_returns_200 PASSED
backend/tests/test_health.py::TestHealthEndpoint::test_health_status_is_healthy PASSED
backend/tests/test_health.py::TestHealthEndpoint::test_health_contains_timestamp PASSED
backend/tests/test_health.py::TestHealthEndpoint::test_health_contains_service_name PASSED
backend/tests/test_health.py::TestHealthEndpoint::test_health_contains_version PASSED
backend/tests/test_health.py::TestApiHealthEndpoint::test_api_health_returns_200 PASSED
backend/tests/test_health.py::TestApiHealthEndpoint::test_api_health_status_is_healthy PASSED
backend/tests/test_health.py::TestApiHealthEndpoint::test_api_health_contains_components PASSED
backend/tests/test_health.py::TestApiHealthEndpoint::test_api_health_components_have_expected_keys PASSED
backend/tests/test_health.py::TestApiHealthEndpoint::test_api_health_keyword_search_always_enabled PASSED
backend/tests/test_health.py::TestApiHealthEndpoint::test_api_health_contains_timestamp PASSED
backend/tests/test_health.py::TestApiHealthEndpoint::test_api_health_contains_version PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_endpoint_exists PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_returns_response_field PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_returns_metadata PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_metadata_contains_process_time PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_metadata_contains_session_id PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_with_custom_session_id PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_missing_query_returns_422 PASSED
backend/tests/test_query.py::TestChatEndpoint::test_chat_get_method_not_allowed PASSED
backend/tests/test_query.py::TestSessionResetEndpoint::test_reset_endpoint_exists PASSED
backend/tests/test_query.py::TestSessionResetEndpoint::test_reset_returns_ok_status PASSED
backend/tests/test_query.py::TestSessionResetEndpoint::test_reset_returns_session_id PASSED
backend/tests/test_query.py::TestUnknownRoutes::test_unknown_route_returns_404 PASSED
backend/tests/test_query.py::TestUnknownRoutes::test_unknown_api_route_returns_404 PASSED

28 passed, 18 warnings in 0.62s

Endpoint Coverage

Endpoint	Tests	Status
GET /	3	✅ All pass
GET /health	5	✅ All pass
GET /api/health	7	✅ All pass
POST /api/chat	8	✅ All pass
POST /api/session/reset	3	✅ All pass
Unknown routes (404)	2	✅ All pass

How to Run

pip install pytest httpx
python -m pytest backend/tests/ -v


##Design Decisions
Mocked dependencies: torch, vertexai, google-cloud, and sentence-transformers are mocked in conftest.py so tests run instantly without GPU, cloud credentials, or heavy installs
FakeAssistant: The NeuroscienceAssistant is replaced with a lightweight fake that returns predictable responses, isolating API layer tests from LLM behavior
Pytest configuration: Added [tool.pytest.ini_options] to pyproject.toml rather than a separate pytest.ini to keep config centralized

[SandeepChauhan00]

PR submitted: #64

28 tests covering all backend endpoints — all passing on Python 3.14. Heavy dependencies are mocked so tests run instantly without GPU or cloud credentials.