And it is from a post of Patrick Smacchia on simple-talk.

Patrick wrote an essay about writing unit testing code in c#, in which I personally found a lot of good points that I could not agree more. For example:

• Not all classes need to be 100% covered by tests or even covered at all.
• The 100% coverage practice is costly only when it forces substandard code to be well designed.

And especially for the second one, I think it is inspirational and encouraging. I faced situations from time to time that for some certain pieces of codes/logic, it was difficult to write a comprehensive test suite to cover all the branches. Honestly, most of time when I faced this, I will choose to leave the coverage not to 100% and accept the fact. But after reading this, from now on, I will try my best to achieve the 100% coverage by not only writing comprehensive test cases, but also refactoring the “difficult” logic to the best designed, intuitive, and enjoyable to read codes.