alt Hacker News> IMO, good tests are relatively immutable. You should be able to have multiple valid implementations. You should add new tests to describe the new functionality of that implementation, however, the old tests should remain relatively untouched.
Taken to extreme this would mean getting rid of unit tests altogether in favor of functional and/or end-to-end testing. Which is... a strategy. I don't know if it is a good or bad strategy, but I can see it being viable for some projects.
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> Taken to extreme this would mean getting rid of unit tests all together in favor of functional and/or end-to-end testing.
The dirty little secret in CS is that unit, functional, and end-to-end tests are all the exact same thing. Watch next time someone tries to come up with definitions to separate them and you'll soon notice that they didn't actually find a difference or they invent some kind of imagined way of testing that serves no purpose and nobody would ever do.
Regardless, even if you want to believe there is a difference, the advice above isn't invalidated by any of them. It is only saying test the visible, public interface. In fact, the good testing frameworks out there even enforce that — producing compiler errors if you try to violate it.
If you can't tell, I actually think functional tests have a lot more value than most unit tests :)
Kent Dodd agrees with me. [1]
This isn't to say I see no value in unit tests, just that they should tend towards describing the function of the code under test, not the implementation.
[1] https://kentcdodds.com/blog/the-testing-trophy-and-testing-c...