The plan was to try and write as many tests as we could for the Constraint classes PHPUnit uses to implement its assertions. [...] Well, our plan didn't work out that way, we didn't really succeed in writing a considerable amount of unit tests. However, it still was a valuable experience, as it turned out the unit tests of the Constraints are a good example of how not to unit test.

He includes three of the major points they came across in their practice development:

• Don't use one single test case class to test several different classes
• Name your tests well
• Avoid to test more than one behaviour in one single test

For each, there's a summary answering the "why" question behind them including an example test (testConstraintIsType) that shows a bad, multiple assertion practice that should be avoided if possible.

He breaks it down into to categories - the good and the bad. Some of the items on either list include:

• static methods (good)
• E_STRICT (bad)
• random passing by reference gone (good)
• replacing is_a() with instanceof (bad)

He also offers some of his personal suggestions for guidelines for future language updates.