def test_has_a_stack_list():
 assert hasattr(io.FileSystem, 'stack'), 'FileSystem should have a stack'
 assert isinstance(io.FileSystem.stack, list), 'FileSystem.stack should be a list'

def test_has_a_stack_list ( ) : assert hasattr ( io . FileSystem , 'stack' ) , 'FileSystem should have a stack' assert isinstance ( io . FileSystem . stack , list ) , 'FileSystem.stack should be a list'
filesystem stack list .