I need to test a number of functions that I have created using PHP 5 which carry out the required database CRUD type actions (SELECT, UPDATE, INSERT, DELETE) which are required by my web application.

I have been looking at PHP unit testing suites such as Simple Test and PHP Unit which seem to offer what I need however I am unsure how I am meant to achieve this, as equivalence partitioning and boundary analysis isn't all that clear. Do I just need to input different variables and vary this? This seems rather pointless as a string that is different may not necessarily make any difference. 

Any guidance on this would be helpful as I have not encountered this before.