How to capture an argument that was passed to a mocked function and return it?

Question

So in the service I am testing, I have a depending service which is taking an object and does some augmenting on it. I want to mock the part the depending service is doing and make the mock return exactly what it's receiving. Problem is I don't have access to that.

I tried something like this:

  val captureMyObject = slot<MyObject>()
  every { serviceX.doSomething(capture(captureMyObject)) } 
  returns captureMyObject.captured

But it fails with: kotlin.UninitializedPropertyAccessException: lateinit property captured has not been initialized

Answer 1

Following oleksiyp comment, I reread the docs. Correct way is:

val captureMyObject = slot<MyObject>()
every { serviceX.doSomething(capture(captureMyObject)) } answers {captureMyObject.captured}