code: def test_add_used_skill(self):
      skills_manager = SkillsManager()
      skill1 = Mock()
      skill2 = Mock()
      skill1.name = "SkillA"
      skill2.name = "SkillB"
      skills_manager.add_skills(skill1, skill2)
  
      # Test adding used skills
      skills_manager.add_used_skill("SkillA")
      skills_manager.add_used_skill("SkillB")
  
      # Ensure used skills are added to the used_skills list
      assert "SkillA" in skills_manager.used_skills
      assert "SkillB" in skills_manager.used_skills
  
imports: from typing import Optional
  from unittest.mock import MagicMock, Mock, patch
  import uuid
  import pandas
  import pytest
  from pandasai.agent import Agent
  from pandasai.helpers.code_manager import CodeExecutionContext, CodeManager
  from pandasai.helpers.skills_manager import SkillsManager
  from pandasai.llm.fake import FakeLLM
  from pandasai.skills import skill, Skill
  from pandasai.smart_dataframe import SmartDataframe
label_desc: Use image node_id 10 for calling the TestSkills obj's underlying member method code with example usage: obj.test_add_used_skill() without return types