单元测试应如何与外部资源一起工作？ 什么是正确的方法？

Question

I have recently learned about unit testing and know that you shouldn't be unit testing external resources. So, that leads me to a problem for testing a simple function that I want to rewrite to the standards of unit testing.

An example of the function is below for simplicity sake:

def longTask(somearg):
  # Check somearg

  # Begin infinite loop
    # Check remote resource loop based on somearg

    # Write results to a database or file

    # Check to break loop

  # Cleanup upon end

I want to make sure the above code has been unit tested (now that I know of unit testing).

My main confusion comes from the fact of how can I unit test simple functions that are making external resource calls when you aren't supposed to unit test external resources?

Note: I have read the other posts about this on SO but those do not answer my question.

Answer 1

 My main confusion comes from the fact of how can I unit test simple functions that are making external resource calls when you aren't supposed to unit test external resources? 

What I usually do in cases such as this is use a mock of some sort. There are some excellent mock packages for python, for instance http://www.voidspace.org.uk/python/mock that make these kind of substitutions of a test object for a real object much easier

For example

    def test_au(self):
        user_id=124
        def apple(req):
            return 104
        with patch('pyramid.security.authenticated_userid', return_value=user_id
):
            authenticated_userid = apple
            self.assertEqual("104", authenticated_userid(self.request).__str__()
)

patch is a method imported from mock. It alters the behaviour of other packages within the scope it is given.

In this example, the predefined library method for authenticated_userid is imported with from pyramid.security import authenticated_userid and works within the pyramid framework. To test that it is returning the correct value after my setup function has run I can "override" the method during the test

Answer 2

Have you considered using something like a Fake object [1] to test your code. You could provide a wrapper/interface for the external resource and for your tests, use a version of that wrapper/interface that offers behavior to facilitate testing.

[1] https://en.wikipedia.org/wiki/Mock_object#Mocks.2C_fakes_and_stubs