How to run lambda function passed to a mockked method?

Question

I wonder whather it's possible to run a lambda function passed as a parameter to a mocked function. And run it whenever the mocked method is called.

I am using Mockk and I imagine the code to be something like this:

class DataManager {
   fun submit(lambda: (Int) => Unit) { ... }
}

...

val mock = mockk<DataManager>()

every { mock.submit(lambda = any()) }.run { lambda(5) }

In my real implementation the datamanager calls a server and runs the lambda as a callback when it recieves a successful response. The lambda happens to be a private method of the class under test.

Answer 1

You need to use a Capture instead of Any.

val dataManager: DataManager = mockk()

every { dataManager.submit(captureLambda()) } answers { lambda<(Int) -> Unit>().invoke(5) }

dataManager.submit { i -> println(i) }

Additionally the the declaration of your function type is invalid.

You have (Int) => Unit when it should be (Int) -> Unit.

Answer 2

Can be solve in the following ways.

with args from answer:

every { dataManager.submit(any()) } answers {
      firstArg<(Int) -> Unit>().invoke(5)
}

or with captureLambda

every { dataManager.submit(captureLambda()) } answers {
      lambda<(Int) -> Unit>().captured.invoke(5)
}