I personally have found it's much more difficult to partially mock out concepts when writing logic in the DB layer though my tooling may have been the weakpoint

I personally have found it's much more difficult to partially mock out concepts when writing logic in the DB layer though my tooling may have been the weakpoint. In a nice application language I can easily isolate specific units of code for direct testing - while every test I write over complex database logic feels like composing a symphony where I need to make sure the horns are coming in on the right pitch and the wind section isn't too early to properly simulate a relatively easy error scenario. Since the application layer is much more naturally aligned with small well isolated chunks of logic it is easier to minimize the volume of code and logic in scope when testing a particular attribute - when that goes into the DB I've always seen things get more complex rapidly.