[nrinaudo]

What do you mean, you should not be testing internal implementations anyway? Does that also mean you don't do unit test, only integration or end-to-end ones, because unit tests are tests of the internal implementation of your software?

[matthewmacleod]

Not quite – most projects have internal interfaces which are relatively stable, and tests should be against those, rather than the internal implementation of those modules.

Unit tests are great, but they should still be testing at the boundary of code modules – if changing the internal implementation of that module breaks a test, it probably isn't testing at the correct level.

[goldenkek]

He means you test pure functions and mutations. You dont stub data sources that your implementations use to see if they were called. tests need to be about enforcement of correct interface exposure. not exact implementations. its one of the most facepalm types of useless testing that ive seen littered around Amazon's Seattle teams due to these Indian managers wanting to make sure the data sources called in every method actually got called and that there is 100% coverage. serves no purpose except to basically make two copies of the code..the test as a doppleganger of the actual code but using stubs.