test: add configuration loading tests

- Add test_config.py with tests for load_settings function
- Add test_config.yaml fixture with test database configuration
- Tests cover: successful loading, file not found error, database URL generation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/fixtures/test_config.yaml

@@ -0,0 +1,10 @@
+# 测试配置
+database:
+  sql_server:
+    host: localhost
+    port: 1433
+    database: TestDB
+    username: test_user
+    password: test_pass
+    driver: "{ODBC Driver 18 for SQL Server}"
+    trust_server_certificate: yes

tests/test_config.py

@@ -0,0 +1,25 @@
+import pytest
+from config.settings import load_settings
+
+
+def test_load_settings_success():
+    """测试成功加载配置文件"""
+    settings = load_settings("tests/fixtures/test_config.yaml")
+    assert settings.database.sql_server.port == 1433
+    assert settings.database.sql_server.host == "localhost"
+    assert settings.database.sql_server.database == "TestDB"
+
+
+def test_load_settings_file_not_found():
+    """测试配置文件不存在时抛出异常"""
+    with pytest.raises(FileNotFoundError):
+        load_settings("nonexistent.yaml")
+
+
+def test_database_url_property():
+    """测试 database_url 属性生成"""
+    settings = load_settings("tests/fixtures/test_config.yaml")
+    url = settings.database_url
+    assert "mssql+pyodbc" in str(url)
+    assert "test_user" in str(url)
+    assert "TestDB" in str(url)