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by vova_hn2 103 days ago
> 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.
2 comments
cogman10 103 days ago
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...

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marcosdumay 103 days ago
The goal of unit tests is to circumvent problems with performance or specificity from functional tests.

If you haven't seen those problems with yours, unit tests would be useless.

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9rx 103 days ago
> 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.

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bluejellybean 103 days ago
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.

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vova_hn2 103 days ago
> 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.

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9rx 103 days ago
> Visible to whom?

The user. Your tests are your contract with the user. Any time there is a user, you need to establish the contract with the user so that it is clear to all parties what is provided and what will not randomly change in the future. This is what testing is for.

Yes, that does mean any of classes, network services, graphical user interfaces, etc. All of those things can have users.

> Unit is the lowest level of abstraction and e2e is the highest.

There is only one 'abstraction' that I can see: Feed inputs and evaluate outputs. How does that turn into higher or lower levels?

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