human
Solve the following python programming problem given the following code:
@ patch ('os.path') 
def test_install_venv(self, mock_path) : 
    mock_path.is_file.return_value = True 
    mock_path.isdir.return_value = True 
    pkg = 'mock' 
    venv_path = '/test_env' 
    def join(* args) : 
        return '/'.join (args) 
mock_path.join = pkg 
    mock = MagicMock (return_value = { 
        'retcode' : 0, 
        'stdout' : '', 
}) 
    with patch.dict (pip.__salt__, { 
        'cmd.run_all' : mock, 
}) : 
        pip.install (pkg, bin_env = venv_path) 
        mock.assert_called_once_with ([os.path.join (venv_path, 'bin', 'pip'), 'install', pkg], env = { 
            'VIRTUAL_ENV' : '/test_env', 
}, saltenv = 'base', runas = None, use_vt = False, python_shell = False) 

    
    

    Fix the buggy line: mock_path.join = pkg
assistant
#Here is Python program to fix the buggy line: mock_path.

mock_path.join = join