If you have an interest in arithmetic and numerical methods, particularly
the implementation of Complex and Float arithmetic, then this message by
Andres Valloud and Juan Vuletich (on the Cuis list) is worth a careful read:

https://lists.cuis.st/mailman/archives/cuis-dev/2019-June/000447.html

The post also contains some interesting discussion of modularity, and of
unit testing for exception behavior.

Dave