How testing Child Themes before upload

Hi!
I made a child theme to twentyfifteen and it passed theme check, but how do i debug the php (wp-config) WITHOUT being drawn back to the wp root? I hope you’ll understand what i mean.

There’s lots of info about child themes, but it’s difficult to find instructions how to find info and rules in how to check them. Can someone please point me a direction where i can find my answers?

Kindly Lillan