Unit testing handling of degraded network stack, file corruption, and other imperfections

Question

I\'m primarily a C++ coder, and thus far, have managed without really writing tests for all of my code. I\'ve decided this is a Bad Idea(tm), after adding new features that subt

Answer 1

It sounds as if you answered your own question.

Mocks/stubs are the key to testing difficult to test areas. For all of your examples, the manual approach of say creating a website with dodgy data, or causing network failure could be done manually. However it would be very difficult and tedious to do so, not something anyone would recommend. In fact, doing some would mean you are not actually unit testing.

Instead you'd use mock/stubs to pretend such scenarios have happened allowing you to test them. The benefit of using mocks is that unlike the manual approach you can guarantee that each time you run your tests the same procedure will be carried out. The tests in turn will be much faster and stable because of this.

Edit - With regards the updated question.

Just as a disclaimer my networking experience is very limited, therefore I can't comment on the technical side of your issues. However, I can comment on the fact you sound as if you are testing too much. In other words, your tests cover too much of a wide scope. I don't know what your code base is like but given functions/objects within that, you should still be able to provide fake input that will allow you to test that your objects/functions do the right thing in isolation.

So lets imagine your isolated areas work fine given the requirements. Just because your unit tests pass does not mean you've tested your application. You'll still need to manually test such scenarios you describe. In this scenario it sounds as if stress testing - limiting network resources and so on are required. If your application works as expected - great. If not, you've got missing tests. Unit testing (more in tie with TDD/BDD) is about ensuring small, isolated areas of your application work. You still need integration/manual/regression etc.. testing afterwards. Therefore you should use mocks/stubs to test your small, isolated areas function. Unit testing is more akin to a design process if anything in my opinion.