如何在Visual Studio（VB.Net和C＃）中对私有功能进行单元测试？

Question

I know it may sound like a silly question as I've heard many saying that you should only do unit testing for public function and indeed, visual basic.net in Visual studio IDE only allows me to do unit testing for public function.

However, I got a public function that is calling to many other private functions. If I do unit testing for that public function, that would be too complicated. I only want to test each private function individually to make sure it works correctly first, before jumping to the parent public function.

One solution I've had in my mind is that I could change all private functions to public ones so that Visual Studio allows me to do unit testing for them. But it is annoying me as I don't want them to be public.

Is there any suggestions you could let me know please?

many thanks in advance.

NTC

Answer 1

If you really can't break the code out into separate classes, you could change all of the private functions to be protected and then create a private class within your test class that inherits from the class you're trying to test (this would be named as a fake or stub, hence my advice to make it private. You don't want code outside of the test class to interact with this). Within your inherited class, create public functions for each of the now protected functions that simply call through to the base and write your unit tests against those instead.

Answer 2

I apologize if this capability is not available in VB:

Create a sub-class of the class you want to test. Ensure that the sub-class has public interfaces to the private functions.

As for "only unit test public functions?" That's horse manure. You test what might fail. For instance, you might have a class with only one public function, and you want to refactor into a set of calls on private functions to decrease the complexity. If you have to refactor your solution for any reason (as one of the comments suggested), then the first step is to have all the pieces of the solution tested that you will have to change during the refactoring.