The Art of Unit Testing

To deal with the issue I mentioned in the post TDD is Hard earlier I bought the book The Art of Unit Testing by Roy Osherove. It helped a lot! Osherove writes plenty about how to make the tests cope with changes in the code and about writing maintainable tests.

He also mentioned Test Coverage tools as a good way to build reliable tests. Making sure every line is covered by a test doesn't test all possible results tho, but it's a good start. For example if you want to test a method that validates email addresses you might just have a RegExp. That row will be covered by the first test you write. Still I wouldn't find it reliable by just making a test with one email address. Here I didn't find any solution in the book, so I'd be interested to hear how you make sure your test is reliable.

How ever, I downloaded the last free version of NCover Explorer (1.4.0.7). It showed to be a very competent tool that let me find a bunch of untested code paths, and also a few completely untested classes. We also added a simple version to our Cruise Control project that gives us a figure with the current coverage (88 % right now). We have not excluded code that are excluded from the unit tests with the Ignore attribute though, so the real coverage is higher. We use the Ignore attribute for some integration tests that require a VPN connection to work.

Among the tips from the book I found the most important one was to have at most one mock object in a test, while other fake objects should be stubs. He also claimed that a test should have only one Assert verifying the outcome, but I'm not sure I agree with that. He is the expert tho, but I guess I need to burn my own fingers before I agree with that.

As a conclusion I would recommend this book to anyone. The one who wants to start doing unit testing will probably get the most from the book, but I think that also the one who is just curious about it and definatly the one who's been doing it for some time (that's me!) will have a good read too. I bet that even the expert might get some new insights while reading it. And it's a quick read - I think I spent less than 10 hours to read it all, except the appendixes.