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/unit/test_config.py

@@ -0,0 +1,47 @@
+"""
+Unit tests for handler_base.config module.
+"""
+import os
+import pytest
+
+
+class TestSettings:
+    """Tests for Settings configuration."""
+    
+    def test_default_settings(self, settings):
+        """Test that default settings are loaded correctly."""
+        assert settings.service_name == "test-service"
+        assert settings.service_version == "1.0.0-test"
+        assert settings.otel_enabled is False
+    
+    def test_settings_from_env(self, monkeypatch):
+        """Test that settings can be loaded from environment variables."""
+        monkeypatch.setenv("SERVICE_NAME", "env-service")
+        monkeypatch.setenv("SERVICE_VERSION", "2.0.0")
+        monkeypatch.setenv("NATS_URL", "nats://custom:4222")
+        
+        # Need to reimport to pick up env changes
+        from handler_base.config import Settings
+        s = Settings()
+        
+        assert s.service_name == "env-service"
+        assert s.service_version == "2.0.0"
+        assert s.nats_url == "nats://custom:4222"
+    
+    def test_embeddings_settings(self):
+        """Test EmbeddingsSettings extends base correctly."""
+        from handler_base.config import EmbeddingsSettings
+        
+        s = EmbeddingsSettings()
+        assert hasattr(s, "embeddings_model")
+        assert hasattr(s, "embeddings_batch_size")
+        assert s.embeddings_model == "bge"
+    
+    def test_llm_settings(self):
+        """Test LLMSettings has expected defaults."""
+        from handler_base.config import LLMSettings
+        
+        s = LLMSettings()
+        assert s.llm_max_tokens == 2048
+        assert s.llm_temperature == 0.7
+        assert 0 <= s.llm_top_p <= 1