第八课按照视频敲代码以后，选择回测模块，报错如下：
策略文件strategies.test_strategy加载失败，触发异常：
Traceback (most recent call last):
File "C:\vnstudio\lib\site-packages\vnpy\app\cta_backtester\engine.py", line 110, in load_strategy_class_from_module
module = importlib.import_module(module_name)
File "C:\vnstudio\lib\importlib__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
File "<frozen importlib._bootstrap>", line 983, in _find_and_load
File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
File "<frozen importlib._bootstrap_external>", line 728, in exec_module
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "C:\Users\Administrator\strategies\test_strategy.py", line 128, in <module>
class NewBarGenerator(BarGenerator):
File "C:\Users\Administrator\strategies\test_strategy.py", line 136, in NewBarGenerator
interval: Interval = Interval.MINUTE
NameError: name 'Callable' is not defined
19:36:52 策略文件加载完成
