MockK mock method returning Interface Future - kotlin

Question

Hello I have following problem.
I am trying to mock call of injected executor
to execute given Callable immediately. Later in test arguments of methods called inside Callable are captured and arguments are asserted. Mock example see bellow.
Maven 3, jdk 10-slim, mockk 1.9
//this task should be executed by executor
private val taskCaptor = slot<Callable<Boolean>>()
private val asyncTaskExecutor: LazyTraceThreadPoolTaskExecutor = mockk<LazyTraceThreadPoolTaskExecutor>().apply {
//this was my 1st try, but resutt was java.lang.InstantiationError: java.util.concurrent.Callable
//every { submit(capture(taskCaptor)) } returns CompletableFuture.completedFuture(taskCaptor.captured.call())
//every { submit(any()) } returns CompletableFuture.completedFuture(true)
every { submit(ofType(Callable::class)) } returns FutureTask<Boolean>(Callable { true })
}
later on I have changed Callable interface to implementation, which I have created in tested class and I got another exception.
With same code as above exceptions was
java.lang.InstantiationError: java.util.concurrent.Future
which is return type of submit method.
Is my approach to mocking wrong?

Answer 1

not sure if this is the best way to implemented but for me it worked this way:
private val taskCaptor = slot<Callable<Boolean>>()
private val asyncTaskExecutor: LazyTraceThreadPoolTaskExecutor = mockk<LazyTraceThreadPoolTaskExecutor>().apply {
every { submit(ofType(Callable::class)) } returns mockFuture
every { mockFuture.get() } returns true
}