test: add comprehensive test suite with 89% coverage

- Add tests for all backend modules: config, database, models, services,
  routes, middleware, and providers
- Separate dev dependencies using dependency-groups
- Update CLAUDE.md with test commands and project structure
- Add .coverage and .pytest_cache to gitignore

88 tests covering:
- Authentication and authorization
- Model routing and key selection
- Async logging with batch processing
- All API endpoints (chat, openai, anthropic, health)
- LiteLLM wrapper (mocked external calls)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/tests/test_routes_openai.py

@@ -0,0 +1,121 @@
+"""Tests for OpenAI native routes."""
+import pytest
+from unittest.mock import MagicMock
+from fastapi.testclient import TestClient
+
+from app.main import app
+from app.models import ClientKey, Provider
+
+
+@pytest.fixture
+def mock_client_key():
+    """Return a valid client key for testing."""
+    return ClientKey(
+        id=1,
+        key="test-api-key",
+        name="test-client",
+        is_active=True,
+        created_at="2024-01-01"
+    )
+
+
+@pytest.fixture
+def mock_openai_provider():
+    """Return a mock OpenAI provider."""
+    return Provider(
+        id=1,
+        name="openai",
+        base_url="https://api.openai.com/v1",
+        api_type="openai",
+        is_active=True
+    )
+
+
+class TestOpenAIChat:
+    """Test /v1/openai/chat/completions endpoint."""
+
+    def test_openai_chat_unauthorized(self):
+        """Test OpenAI chat without auth."""
+        client = TestClient(app)
+        response = client.post(
+            "/v1/openai/chat/completions",
+            json={"model": "gpt-4o", "messages": [{"role": "user", "content": "hi"}]}
+        )
+        assert response.status_code == 401
+
+    def test_openai_chat_success(self, mock_client_key, mock_openai_provider):
+        """Test successful OpenAI chat."""
+        from app.middleware.auth import get_current_client
+        from app.services.router import ModelRouter
+        from app.services.key_selector import key_selector
+        from app.services.logger import async_logger
+        from app.providers.litellm_wrapper import LiteLLMWrapper
+
+        app.dependency_overrides[get_current_client] = lambda: mock_client_key
+
+        mock_response = MagicMock()
+        mock_response.model_dump.return_value = {
+            "id": "chatcmpl-test",
+            "choices": [{"message": {"content": "Hello!"}}]
+        }
+
+        original_get_provider = ModelRouter.get_provider
+        original_get_key = key_selector.get_next_key
+        original_chat = LiteLLMWrapper.chat_completion
+        original_log = async_logger.log
+
+        async def mock_get_provider(name):
+            return mock_openai_provider
+
+        async def mock_get_key(provider_id):
+            return MagicMock(key="sk-test")
+
+        async def mock_chat(*args, **kwargs):
+            return (mock_response, 10, 20)
+
+        async def mock_log(entry):
+            pass
+
+        ModelRouter.get_provider = staticmethod(lambda name: mock_get_provider(name))
+        key_selector.get_next_key = mock_get_key
+        LiteLLMWrapper.chat_completion = staticmethod(lambda *a, **k: mock_chat(*a, **k))
+        async_logger.log = mock_log
+
+        try:
+            client = TestClient(app)
+            response = client.post(
+                "/v1/openai/chat/completions",
+                json={"model": "gpt-4o", "messages": [{"role": "user", "content": "hi"}]},
+                headers={"Authorization": "Bearer test-api-key"}
+            )
+            assert response.status_code == 200
+        finally:
+            ModelRouter.get_provider = original_get_provider
+            key_selector.get_next_key = original_get_key
+            LiteLLMWrapper.chat_completion = original_chat
+            async_logger.log = original_log
+            app.dependency_overrides.clear()
+
+
+class TestOpenAIModels:
+    """Test /v1/openai/models endpoint."""
+
+    def test_openai_models_success(self, mock_client_key):
+        """Test list OpenAI models."""
+        from app.middleware.auth import get_current_client
+
+        app.dependency_overrides[get_current_client] = lambda: mock_client_key
+
+        try:
+            client = TestClient(app)
+            response = client.get(
+                "/v1/openai/models",
+                headers={"Authorization": "Bearer test-api-key"}
+            )
+            assert response.status_code == 200
+            data = response.json()
+            assert data["object"] == "list"
+            for model in data["data"]:
+                assert model["owned_by"] == "openai"
+        finally:
+            app.dependency_overrides.clear()