code: def test_gitpython_not_installed(self):
      with patch.dict("sys.modules", {"git": None}):
          repo = GitRepo(".")
          self.assertFalse(repo.is_valid())
  
file_path: streamlit/lib/tests/streamlit/git_util_test.py
imports: import unittest
  from unittest.mock import patch
  from git.exc import InvalidGitRepositoryError
  from streamlit.git_util import GITHUB_HTTP_URL, GITHUB_SSH_URL, GitRepo
label_desc: Use image node_id 6 for calling the GitUtilTest obj's underlying member method code with example usage: obj.test_gitpython_not_installed() without return types