Probably my favorite book on software testing would be "Lessons Learned In Software Testing", which is more a discussion about the people and process aspects of software testing instead of specific techniques. If you're interested in testing as a profession rather than merely as a job, it's worth a read.
I wanted to recommend google test documentation... which is certainly not agnostic :(
I put together a reading list of the best writing on automated testing I know. Most of this is agnostic wrt the language you use, though of course examples are written in a language.
## Monographs
Test Driven Development By Example (Kent Beck)
Unit Testing: Principles, Practices, and Patterns (Vladimir Khorikov)
The Art of Unit Testing 2nd ed (Roy Osherove)
Working Effectively with Legacy Code (Michael Feathers)
## Various resources
[Unit Testing Best Pratices](https://www.youtube.com/watch?v=k_ItB5btREU&t=2931s&ab_chann...) (Vladimir Khorikov)
[Testing Without Mocks: A Pattern Language](https://www.jamesshore.com/v2/blog/2018/testing-without-mock...) (James Shore)
[TDD Lunch & Learn](https://www.jamesshore.com/v2/projects/lunch-and-learn) (James Shore)
[Test Driven Development - What? Why? And How?](https://www.youtube.com/watch?v=llaUBH5oayw&ab_channel=Conti...) (Dave Farley)
[The 3 Types of Unit Test in TDD](https://www.youtube.com/watch?v=W40mpZP9xQQ&t=22s&ab_channel...) (Dave Farley)
[TDD and the Lump of Coding Fallacy](https://www.geepawhill.org/2018/04/14/tdd-the-lump-of-coding...) (Geepaw Hill)
## Against Unit Tests
[Why Most Unit Testing is Waste](https://rbcs-us.com/documents/Why-Most-Unit-Testing-is-Waste...) (James O Coplien)
[On unit testing and TDD](https://www.youtube.com/watch?v=21JlBOxgGwY&ab_channel=JeruS...) (Jonathan Blow)