python - 如何模拟输入函数并检查是否引发异常

Question

我有一个使用 input 函数的函数，如下所示:

def get_valid_input(input_str: str, valid_options: tuple):
    while True:
        response = input(input_str)
        if response in valid_options:
            return response
        raise InvalidOptionException('Invalid option')

我需要测试当响应不是有效选项时是否会引发异常InvalidOptionException(它简单地扩展了Exception)。我有以下测试:

class UtilTest(unittest.TestCase):
    @patch('builtins.input', lambda: 'a')
    def test_when_input_is_invalid_then_exception_is_raised(self):
        self.assertRaises(
            InvalidOptionException,
            get_valid_input,
            '', ('y', 'n')
        )

但是，当我运行测试时，出现以下错误:

Error
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/mock.py", line 1179, in patched
    return func(*args, **keywargs)
  File "/Users/user/mathsistor/chumme/test/test_util.py", line 13, in test_when_input_is_invalid_then_exception_is_raised
    '', ('y', 'n')
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/case.py", line 728, in assertRaises
    return context.handle('assertRaises', args, kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/case.py", line 177, in handle
    callable_obj(*args, **kwargs)
  File "/Users/user/mathsistor/chumme/util.py", line 14, in get_valid_input
    response = input(input_str)
TypeError: <lambda>() takes 0 positional arguments but 1 was given

我该如何解决这个问题？

Answer 1

input 函数采用一个参数(提示字符串)。要模拟它，您必须使用带有一个参数的函数/lambda:

@patch('builtins.input', lambda _: 'a')

当您不打算使用参数时，通常使用下划线。