Ask HN: Best resources to learn code testing

I have more than a decade of experience in software development (now team lead at a FAANG, working on higher level systems) and I embarrassingly realize I still do not know how to write good tests and testable code. Specifically:

- How to structure production code so that it’s testable

- How to effectively deal with dependency injection for testing

- The surface area and granularity of unit tests (what behavior should be tested vs not)

- When to use mocks/stubs/fakes

What are the best resources to fix my gaps? Open to books, courses, videos, etc.