How can we mock lambdas in Kotlin? Eg. `(T) -> ...

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[chetsachdeva]

How can we mock lambdas in Kotlin? Eg. (T) -> Unit

[louiscad]

Yes, here's the manual way: { t -> }

[poohbar]

#C9EJFT6DB

[chetsachdeva]

I'm trying to understand how do I use when then for mocking lambdas. I see doAnswer on the web but need more information.

[chetsachdeva]

I want to test the Presenter. The function in my Presenter looks like this:

override fun search(query: String) {
        interactor.search(query) { model ->
            view.render(searchState(model))
        }
    }

interface Interactor {
        fun search(query: String, publish: (SearchModel) -> Unit)
}

[gildor]

I don’t think that one need mocking there. What exactly do you want to check? You can check that interactor method is called and you can return some value for model

[chetsachdeva]

I want to perform a whenever thenReturn on this method containing lambda

[gildor]

Just add implementation to lambda, why do you need mocking here?:

val myMockLambda = { model ->
   return when(model) {
      model.something() -> someResult
      model.anythingElse() -> anotherResult
   }
}

[gildor]

I would use this approach, but nothing prevent you from mocking lambda, it’s just an interface under the hood

[chetsachdeva]

Coz the function returns Unit and I cannot return Void for mocking

[gildor]

Return Unit instead

[chetsachdeva]

Yea, Unit doesn't work either

[gildor]

do you use Mockito?

[chetsachdeva]

Yes

[gildor]

Works on Mockito Kotlin
https://github.com/nhaarman/mockito-kotlin

https://github.com/nhaarman/mockito-kotlin/blob/35f728defa11db9a90f61186be03bd009d80d424/tests/src/test/kotlin/test/VerificationTest.kt#L51

[chetsachdeva]

Ok lemme try this. Thanks 🙂

[chetsachdeva]

val publish = mock<(SearchModel) -> Unit>()

whenever(interactor.search("", publish)).thenReturn(publish.invoke(SearchModel.Init))

Getting UnfinishedStubbingException here

[gildor]

hmm? You use mocking in a wrong way.

[gildor]

whenever is like template

[gildor]

and this method called by presenter

[gildor]

You can do something like:

val interactor = mock<MyInteractor>()
whenever(interactor.search("", any())).thenReturn(SearchModel.Init)

[chetsachdeva]

@Test
    fun search() {
        val publish = mock<(SearchModel) -> Unit>()

        whenever(interactor.search("", publish)).doAnswer { publish(SearchModel.Init) }

        presenter.search("")

        verify(view).render(SearchState.Init)
    }

[gildor]

No, it’s wrong. Check documentation of whenever

[gildor]

I don’t understand why do you need mock publish at all in this case

[gildor]

if you just want to return something from lambda just return it, using mocking or manually

[chetsachdeva]

the search function takes in a lambda and I want to return some value from it

[gildor]

Could you show some minimal example, how you presenter work, You problem that lambda passed to interactor is passed from presenter

[gildor]

I think your problem is not in mockito or in lambda that returns Unit

[gildor]

Try to write minimal example and I can try to help you, now looks like you on a wrong way

[chetsachdeva]

override fun search(query: String) {
        interactor.search(query) { model ->
            view.render(model.state())
        }
    }

[chetsachdeva]

I want to test this function

[chetsachdeva]

The callback is returned from the interactor ie of type (SearchModel) -> Unit

[gildor]

class SimpleInteractor : Interactor {
  override fun search(query: String, lambda: (SearchModel) -> Unit) {
      lambda(SearchModel.Init)
   }
}

[gildor]

Maybe this simple interactor can help you?

[chetsachdeva]

Yes this is how I've implemented my interactor

[gildor]

That just call your callback

[gildor]

also, you can improve it and pass required state

[gildor]

So why you need mocking?

[chetsachdeva]

Maybe not. I want to mock interactor.search(query: String, (SearchModel) -> Unit)

[gildor]

for what?

[chetsachdeva]

Because the presenter calls it and interactor is being mocked

[gildor]

but why? I mean just pass this SimpleInteractor to presenter

[gildor]

looks like your test check view state

[gildor]

you do not check Interactor

[chetsachdeva]

May I DM you the github code reference?

[gildor]

would be better to provide some self contained sample, but you try show you existing code

[chetsachdeva]

Thanks! That'd be really helpful 🙂