initialized variable

Author: Victoria Hall

tests/utils/testutils_docker.py

@@ -133,7 +133,10 @@ def create_container(self, image_repo: str, image_url: str,
 
         function_path = "/home/site/wwwroot"
 
-        configs.libraries.append('azurefunctions-extensions-base')
+        if configs.libraries:
+            configs.libraries.append('azurefunctions-extensions-base')
+        else:
+            configs.libraries = ['azurefunctions-extensions-base']
         install_libraries_cmd = []
         install_libraries_cmd.extend(['pip', 'install'])
         install_libraries_cmd.extend(configs.libraries)