I just want to raise my concern about the security issues the current implementation provides. At a glance the update method provides a simple way to execute arbitrary SQL.
No matter how hard you try. If queries are dynamically created, you (or your lib's user) will most certainly miss a spot were an attacker cloud sneak an offensive query.
You fixed the $i, but what about $table? What about $conditions's keys?
See the problem? And we are just talking about a single method ;-)
TL;DR - it does everything PDO does (thanks to class inheritance) but also has some nice short-hand methods for getting jobs done quicker. DRY and KISS.
There aren't any, currently. These libraries are ripped from an in-house framework which has some tests already, but none for the classes we extracted. We created the tests folder in anticipation of actually writing some.
Please be aware