It's a good idea to run Unit Tests for mission critical routines, e.g. with https://github.com/sebastianbergmann/phpunit/. You can read more about it at http://phpunit.de/manual/current/en/index.html
Of course it's much more work but it's also great once you have it up and running.
Many PHP Frameworks are using Unit Tests now and have PHP Unit built in.
Manuel Lemos - 2013-05-31 15:45:00 - In reply to message 1 from Ralf Strehle
Right, as I said in the ideal world you should always create tests for all the code you use to catch bugs as soon as possible. If you do not have time to create extensive tests, just do that, focus in the most critical code that can fail.