A colleague of mine (Roman Lyashenko) can touch base today on what is new in upcoming Drupal 8 in terms of Unit testing.
He is prepared to dive into the general history of the "unit testing". To answer next “What is unit testing?”, “Where it came from?”, “How old is it?” and “Who was at the forefront of unit testing?”.
Also he can talk about unit testing in Drupal 7 and look on unit testing advantages and disadvantages. And he will show you how to write tests for Drupal 7 using SimpleTest module.
Then he will compare unit test for Drupal 7 with Drupal 8 and will write brand new unit test for Drupal 8 core, using PHPUnit. And we'll look what was changed in Drupal 8.
See you :)