How to call a lambda callback with mockk

Question

I create a mock of a class with mockk. On this mock I now call a method that gets a lambda as a parameter.

This lambda serves as a callback to deliver state changes of the callback to the caller of the method.

class ObjectToMock() {     fun methodToCall(someValue: String?, observer: (State) -> Unit) {         ...     } } 

How do I configure the mock to call the passed lambda?

Answer 1

You can use answers:

val otm: ObjectToMock = mockk() every {  otm.methodToCall(any(), any())} answers {     secondArg<(String) -> Unit>().invoke("anything") }  otm.methodToCall("bla"){     println("invoked with $it") //invoked with anything } 

Within the answers scope you can access firstArg, secondArg etc and get it in the expected type by providing it as a generic argument. Note that I explicitly used invoke here to make it more readable, it may also be omitted.