Unit Testing Best Practices

With the agile shift in software development, unit testing has become more and more important.
I like to say that a good programmer is one who knows how to write good unit tests.
A good unit test grants that tested code is correct, testable, readable, reasonable and even elegant!

So how to write good unit tests?

This is my personal best practices list:

• always use tdd: it grants that the interfaces of your classes (i.e. your api) are created in a real life scenario; testability improves code readability and inner structure, giving it a simple design
  
• use data builders: tests require to create many objects; use data builders to build them; style your test building code defining your own dsl for data building
  
• don't use db-unit, use db builders: db-unit context files are external to the tests, making them less readable and self-contained; these files duplicate code and are hard refactor and maintain (does eclipse refactor automatically an xml/excel ?); so apply the builder pattern to create db objects in java too
  
• use light-weight mock: don't try to verify the internal behaviour of a mock, just mock its external behaviour; digging into the internals of a mock exposes to much information making the test fragile; most of the time you can check the correctness of the class under test just by checking it externally (by the way my favourite mocking library is mockito)
• write readable asserts: use a matcher library such as hamcrest or a dsl like fest-test
  
• use dsl when possible: there are nice libraries out there (time4tea, fest-reflect) that can make your test (or actual) code more fluent, and you can easily create your own (i did a small one for date manipulation, maybe i will post it later on)

That's it.

So go unit testing right now :)