How about taking production issues log and directly linking to how many of them could have been easily covered in unit test layer? Ex. invalid data inputs.

In one of projects, we implemented a similar metric to research and understand that in the absolute absence of unit tests how much issues are coming back from users in production which could have easily be baked in a unit test suite.

How about taking production issues log and directly linking to how many of them could have been naturally covered in unit test layer? Ex. invalid data inputs.

In one of projects, we implemented a similar metric to research and understand that in the absolute absence of unit tests how much issues are coming back from users in production which could have easily be baked in a unit test suite.