[ElatedOwl]

Spot on with cost, as with everything you have to be pragmatic.

Tests are great for:

* High risk items (large consequence when it goes wrong)

* Documentation

* Weird unintuitive things

We had a C# project recently that needs to detect changes between a DTOs properties. At implementation, all the comparisons would be done over value types, but if someone added a reference type that didn't properly implement equality this would silently fail (likely for months). Good case for adding a test that ensures the change detection works for all properties.