Hi,
this is something I know I should embrass in my coding projects but, due to lack of knowledge and my legendary lazyness, I do not do.
In fact, when I do them, I feel like overloaded and I finally give up.
What I am looking for is a good book/tutorial on how to really write good tests -i.e useful and covering a large spectrum of the code -.
Regards
I would suggest taking a look at 'katas' - in particular testing katas. Without knowing what language you use, it's hard to give a more concrete answer.
http://blog.objectmentor.com/articles/2009/11/21/whats-all-this-nonsense-about-katas
Excellent book that covers unit tests for legacy code in particular is Michael Feather's "Working Effectively with Legacy Code"
Roy Osherove's The Art of Unit Testing, especially if you're working in .NET.
Hard to know what language or platform you mean? In regards to .Net Test-Driven Development in Microsoft® .NET. Provides you TDD principles and practices with examples. Have a copy at home and the office. Used it as a primer before getting into TDD and NUnit myself .
If you are looking for a good book going over how to Unit Test I would recommend Kent Beck's : Test Driven Development: By Example. He is the person who really started the idea of Unit Testing, so regardless of language this would be a great book to read to get a good foundation.
Also, Don't let the title discourage you. It does talk about TDD, but it's really just a good easy overview, of how to write effective unit tests, and how they should affect your design which is a key component of writing unit tests.