How to mock a method with lambda argument, e.g. `...

# mockk

[David Kubecka]

How to mock a method with lambda argument, e.g. AsyncTaskExecutor#submit? Currently I'm doing this

val taskExecutor: AsyncTaskExecutor =
        mockk {
            every { submit(captureLambda()) } answers {
                CompletableFuture.completedFuture(lambda<() -> Int>().invoke())
            }
        }

but getting

Caused by: java.lang.ClassCastException: class java.lang.Object cannot be cast to class kotlin.Function (java.lang.Object is in module java.base of loader 'bootstrap'; kotlin.Function is in unnamed module of loader 'app')

I should probably use hint but not sure how exactly.

[David Kubecka]

@Mattia Tommasone Do you have any idea how lambda arguments should be captured invoked? Sorry for direct mention 🙂

[David Kubecka]

I see the problem now. captureLambda() is intended only for Kotlin lambdas (which implement the Function interface). For functional interfaces (Runnable in my case) one must use the generic capture(slot) technique.