Maintainability
The cost of writing tests should be lower than the cost of bugs.
Tests should not primarily focus on common paths. When adding features, all classified test cases must work. When modifying, removing, or adding features, all classified test cases must remain functional.
Code Tests
Code Test Notion

Basically test code is production code
Treat test code like production code
You have to read and maintain test code, too.
https://blog.ploeh.dk/2025/12/01/treat-test-code-like-production-code/
Continuous Test Improvement
On Continuous AI for Test Improvement
Ever since we started working on “task-oriented programming” (aka vibe coding) in 2023, our group at GitHub Next have been throwing around ideas related to “continuous” task…
https://dsyme.net/2025/08/27/on-continuous-test-improvement/

Too much of a good thing: the trade-off we make with tests | nicole@web
I've worked places where we aspired to (but did not reach) 100% code coverage.
We used tools like a code coverage ratchet to ensure that the test coverage always went up and never down.
This had a few effects.
https://ntietz.com/blog/too-much-of-a-good-thing-the-cost-of-excess-testing/

Seonglae Cho