Every single developer I have met in my carreer has written his own framework and every single one of them was full of workarounds to avoid several serious mistakes in the design of the framework, which he initially did not have time to fix, and now cannot afford to fix for fear of creating more errors.
I've never seen a homemade framework that implemented any kind of automated testing.
It's simply scary how many developers waste months of developing time just so they can write some code themselves, knowing that what they write will not be up to scratch. It usually takes a new employee to look at the code before they realize what they did wrong, but by that time, again, it's not an option to fix it.
So, do yourself a favour, go with an existing framework. Sure, it will not work they way you think it should be done, but realistically; you are not a framework designer, you have not thought it through. They have, and they have already dealt with all the poop that you have probably not even seen before.