Hello, i have a problem with mockin a List of mock...

# mockk

[Daniele Andreoli]

Hello, i have a problem with mockin a List of mock. I’m tring to mock this type:

@MockK
lateinit var mockAnalyticsReporters: List<AnalyticsReporter?>

when using this I recieve this strange error:
class kotlin.Unit cannot be cast to class java.lang.Boolean (kotlin.Unit is in unnamed module of loader 'app'; java.lang.Boolean is in module java.base of loader 'bootstrap')
java.lang.ClassCastException: class kotlin.Unit cannot be cast to class java.lang.Boolean (kotlin.Unit is in unnamed module of loader 'app'; java.lang.Boolean is in module java.base of loader 'bootstrap')
at io.mockk.renamed.java.util.Iterator$Subclass5.hasNext(Unknown Source)
I actually can’t understand what this means. I’m not a very well tester so i need some help. Thanks.

[Mattia Tommasone]

that error message doesn’t seem related to the mock instantiation, but rather to casting something to Boolean

[Daniele Andreoli]

Yes but I don’t have anything that matches that return type. I mean, i use that mock in this way:

coEvery { mockAnalyticsReporters.logAnalyticEvent(mockEvent) } answers { }

where`mockEvent` is :

@MockK
lateinit var mockEvent : AnalyticsEvent

[Daniele Andreoli]

the method is an extension function made like this:

fun <T : AnalyticsReporter> List<T?>.logAnalyticEvent(event: AnalyticsEvent) = forEach { reporter ->
        reporter?.logEvent(event)
    }

[Mattia Tommasone]

that empty answers block doesn’t look right to me
does logAnalyticEvent return Boolean?

[Mattia Tommasone]

i’m guessing it does, and if it does, when you mock the method you should be returning a Boolean in the answers block

[Daniele Andreoli]

actually as you can see in the method above that method returns Unit.

[Daniele Andreoli]

also the last line of the stack trace seems related to something mockk does:
at io.mockk.renamed.java.util.Iterator$Subclass5.hasNext(Unknown Source)

[Mattia Tommasone]

also I don’t really see the point of mocking a List
maybe what you want to do is building a list of mocks

[Mattia Tommasone]

I mean, I don’t think what you want to test is that the List class behaves as you expect

[Daniele Andreoli]

Ok, i have to test the code in which this list is called and is a dependency so i have to mock a list. Even without a @MOckk annotation that code returns that problem.. The ext function reciever is a list so I have to mock that list. I actually suspect that the problem could be the List and the forEach. but it’s jsut a guess.

[Mattia Tommasone]

what I’m saying is that IMHO your mock should be something like
val mockAnalyticsReporters = listOf(mockk<AnalyticsReporter>())

[Daniele Andreoli]

Ok, thanks. I’ll try it.

[Klitos Kyriacou]

The function you're trying to test is defined like this:

fun <T : AnalyticsReporter> List<T?>.logAnalyticEvent(event: AnalyticsEvent) = forEach { ... }

and the forEach call relies on the receiver list's iterator's hasNext. But you've mocked that receiver and haven't told the mock what to do with iterator() and hasNext().

[Daniele Andreoli]

@Klitos Kyriacou oh, i see…thanks for the explanation. I will look better into it. 🙂