alt Hacker News> 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.
Replies
> The dirty little secret in CS is that unit, functional, and end-to-end tests are all the exact same thing.
I agree that the boundaries may be blurred in practice, but I still think that there is distinction.
> visible, public interface
Visible to whom? A class can have public methods available to other classes, a module can have public members available to other modules, a service can have public API that other services can call through network etc
I think that the difference is the level of abstraction we operate on:
unit -> functional -> integration -> e2e
Unit is the lowest level of abstraction and e2e is the highest.
Yep, the 'unit' is size in which one chooses to use. The exact same thing happens when trying to discuss micro services v monolith.
Really it all comes down to agreeing to what terms mean within the context of a conversation. Unit, functional, and end-to-end are all weasel words, unless defined concretely, and should raise an eyebrow when someone uses them.