For me that depends on the changes made and the situation.
For BfA I tested my addons with no other addons running to make sure loading process is correct and tested the "main" functionality. Still a few errors made it to Prepatch and I had to push a few updates.
Normally I dont touch the core of the loading process of my addons. I've created a "common" part that all my addons share. With BfA I touched it for the first time in a long time so I ran way more tests than usual.
That means for small changes and additions I dont run a full test nor many tests. For example I've added "connected realms" to my money broker and pushed the update without deeper tests other than checking on a few realms if the sum seems right.
"Luckily" my addons are not that popular so that most errors are never reported before I run into them myself