Why do you want to mock String Just give input and check out

Question

Why do you want to mock String Just give input and check output Something like ``` assertEquals HI hi toUpperCase assertEquals 1 1 toUpperCase ``` It s easy to test function without side effects If a function has side effects you should probably refactor it to make testable Always depends on your case

khoatd191 · Answer

Thank you

khoatd191 · Answer

Assume that we have a validation function to validate user name in ValidationExtensions String validatexxx Then in your presenter you have some code for each result `true` or `false` and call update view so I want to do something like when abc validatexxx thenReturn true to avoid dependency for ValidationExtensions

khoatd191 · Answer

but cannot call `when` cause that String can t be mocked

khoatd191 · Answer

do you have any ideas how to refactor it

Max Russek · Answer

Kotlin extensions compile down to static functions and cannot be mocked Unfortunately this means that you have to get that validation logic from an injected dependency and can t use it as an extension function

Max Russek · Answer

Personally I was hoping in the future it would be possible to import extension methods from an injected dependency somehow like implicits in Scala

gildor · Answer

Don t think that implicits is good solution It can be useful but you getting a lot of problems on big scale

gildor · Answer

< khoatd191> I still not sure what is your problem Just test `String isValidUsername ` separately from your presenter To test presenter do not mock `abc` but provide value from outside for example by mocking View interface

gildor · Answer

Or build some abstraction level for validators and provide it to presenter

khoatd191 · Answer

But assume that we have a lot of extension functions String Context Activity Int Bitmap etc so how many abstraction class we need and if we do that look like we re losing the benefit of extension in Kotlin

Max Russek · Answer

< gildor> I agree that implicits are a poor way of solving the problem but it would be nice to import extensions that could be dynamically dispatched from an object For example ``` interface Validator fun String isValid Boolean class Presenter val validator Validator fun present if user name isValid ```

gildor · Answer

I don t think that extensions is better here than any common Interface Also validator can be much more complicated and Interface can hide this complexity And you don t need special language feature for that you can just use DI to inject required validator

gildor · Answer

Oh I see what you mean

Max Russek · Answer

I could see that there might have to be something like `import validator isValid` or something like that

gildor · Answer

This syntax would be helpful in some cases it s true Not a big difference comparing with this tho ``` interface Validator fun isValid value String Boolean ```

gildor · Answer

Yes I understand now what you mean

Max Russek · Answer

I think the Arrow Kategory people had a KEEP up for something like this a while ago but that included implicit dependency injection a la Haskell Scala and that seems like taking it too far

gildor · Answer

Anyway it s actually very subtle difference that also requires injection of dependencies So I don t think that it can solve < khoatd191> problem < khoatd191> to make your code testable you need some abstractions Extension functions and static methods is not abstraction it s peace of particular logic To make code testable you should use dependency injection of validators And it s not a problem of extensions You can use extensions but you want actually replace behaviour of extension and it s impossible without injection of dependencies

gildor · Answer

< khoatd191> gt how many abstraction class we need You need abstraction only in case when you want transparently replace one behaviour logic with another one If you don t need validator abstraction in your presenter and extension function `String isValidUsername ` is enough for you just use it Write unit test for function itself to check your username validation logic and just provide different input to presenter it should be easy because you probably have View interface that returns current value of `field` that later will be passed to validator and return result depending on content of your field So to test your code you don t need to mock String mock extension functions and Type Classes

khoatd191 · Answer

I wonder should we use this <https github com nhaarman mockito kotlin>

khoatd191 · Answer

so we do not need abstraction for extensions kotlin

gildor · Answer

Mockito Kotlin just provides some API improvements for Mockito and wrappers to work with non nullable types in KLotlin Mockito cannot mock static members Powermock can do that But anyway mock of statics considered as bad practice by many developers including me Again it s not Kotlin specific in java you have exactly the same with static methods

gildor · Answer

And one more time I don t see any reasons to mock anything in your case

khoatd191 · Answer

hmm you re right

oleksiyp · Answer

try this one <http mockk io extension functions>