test: add unit tests for handler-base

- tests/conftest.py: Pytest fixtures and configuration
- tests/unit/test_config.py: Settings tests
- tests/unit/test_nats_client.py: NATS client tests
- tests/unit/test_health.py: Health server tests
- tests/unit/test_clients.py: Service client tests
- pytest.ini: Pytest configuration

tests/conftest.py

@@ -0,0 +1,76 @@
+"""
+Pytest configuration and fixtures.
+"""
+import asyncio
+import os
+from typing import AsyncGenerator
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+
+# Set test environment variables before importing handler_base
+os.environ.setdefault("NATS_URL", "nats://localhost:4222")
+os.environ.setdefault("REDIS_URL", "redis://localhost:6379")
+os.environ.setdefault("MILVUS_HOST", "localhost")
+os.environ.setdefault("OTEL_ENABLED", "false")
+os.environ.setdefault("MLFLOW_ENABLED", "false")
+
+
+@pytest.fixture(scope="session")
+def event_loop():
+    """Create event loop for async tests."""
+    loop = asyncio.new_event_loop()
+    yield loop
+    loop.close()
+
+
+@pytest.fixture
+def settings():
+    """Create test settings."""
+    from handler_base.config import Settings
+    return Settings(
+        service_name="test-service",
+        service_version="1.0.0-test",
+        otel_enabled=False,
+        mlflow_enabled=False,
+        nats_url="nats://localhost:4222",
+        redis_url="redis://localhost:6379",
+        milvus_host="localhost",
+    )
+
+
+@pytest.fixture
+def mock_httpx_client():
+    """Create a mock httpx AsyncClient."""
+    client = AsyncMock()
+    client.post = AsyncMock()
+    client.get = AsyncMock()
+    client.aclose = AsyncMock()
+    return client
+
+
+@pytest.fixture
+def mock_nats_message():
+    """Create a mock NATS message."""
+    msg = MagicMock()
+    msg.subject = "test.subject"
+    msg.reply = "test.reply"
+    msg.data = b'\x82\xa8query\xa5hello\xaarequest_id\xa4test'  # msgpack
+    return msg
+
+
+@pytest.fixture
+def sample_embedding():
+    """Sample embedding vector."""
+    return [0.1] * 1024
+
+
+@pytest.fixture
+def sample_documents():
+    """Sample documents for testing."""
+    return [
+        {"text": "Python is a programming language.", "source": "doc1"},
+        {"text": "Machine learning is a subset of AI.", "source": "doc2"},
+        {"text": "Deep learning uses neural networks.", "source": "doc3"},
+    ]