So now I have come to the conclusion like many others that having some way of constantly testing your code is good practice since it enables fewer people to be involved (colleges and customers alike) by simply knowing what's wrong before someone else finds out the hard way.

I've heard and read some about Unit Testing and understand what it's supposed to do and all. The there are so many different types of bugs. It can be everything from web browser not being able not being able to send correct values, javascript failing, a global function messing up a piece of code somewhere to a change that looked good when testing it out but fails in some special case which was hard to anticipate. My simply finding these errors I learn to rarely repeat them again, but there seems to always be new bugs to be found and learnt from.

I would guess maybe the best practice would be to run every page and it's functions a couple of times, witness the result and repeat this in Firefox, Chrome and Internet Explorer (and all smartphones apparently) to make sure it works as intended. However this would take quite some time to do consider I don't work with patches/versions and do little fixes here and there a couple of times per week.

What I prefer would be some kind of page I can just load that tests as much things as possible to make sure the site works as intended. Basicly just run a lot of cURL's with POST-values and see if I get expected result. But how would I preferably not increase the IDs of every mysql rows if I delete these testing rows? It feels silly to be on ID 1000 with maybe 50 rows in total.

If I could build a new project from scratch I would probably implement some kind of smooth way to return a "TRUE" on testing instead of the actual page. But this solution would for the moment being have to be passed on existing projects.

My question
What would you recommend to be the best way to test my site to make sure that existing functions does their job upon editing the code? Should I consider to implement a lot of edits first, then test manually the entire code to make sure it still works? Is there any nice way of testing codes without "hurting" the ID columns?

Extra thoughs
Would it be a good idea to associate all of my files to the different parts of my site which they affect? For instance if I edit home.php I will through documentation test if my homepage's start works as intended since it's the only part of my site it should affect.