"A Drupal Module Developer's Guide to SimpleTest" - http://www.lullabot.com/articles/drupal-module-developer-guide-simpletest
"An Introduction to Unit Testing in Drupal" - http://www.lullabot.com/articles/introduction-unit-testing
Curioso como esses links me passaram despercebidos ao longo de meses desenvolvendo com Drupal, mas é uma ótima referência para quem já percebeu o valor de se testar as coisas..rsrs
Falando sobre o valor disso, segue um trecho:
"Writing unit tests helps produce higher quality code on many levels.
* The availability of tests helps detect the introduction of bugs whenever the programmer adds new features or refactors the code. This is called regression testing.
* Tests also serve as a source of documentation about what code is really expected to do.
* The act of writing the tests challenges the programmer to consider possible edge cases and their consequences.
* Last but not least, the act of writing tests encourages the programmer to write code in small chunks that can be tested independently."