How to mock a method with functional arguments in Scala?

mocking, scala

Solution

This looks ugly, but hopefully it can help you to find good solution:

import org.scalatest.mock.MockitoSugar
import org.mockito.Mockito._

trait Collaborator {
   def doSomething(t: => Thing)
}

trait Thing

new MockitoSugar {
     // setup
     val m = mock[Collaborator]
     val t = mock[Thing]

     m.doSomething(t)

     classOf[Collaborator].getMethod("doSomething", classOf[Function0[_]]).invoke(
        verify(m), 
        new Function0[Thing] { 
            def apply() = null
            override def equals(o: Any): Boolean = t == o.asInstanceOf[Function0[Thing]].apply() 
      })
}

Problem

I'm trying to mock a method call that takes a call-by-name argument: ``` import org.scalatest.WordSpec import org.scalatest.mock.MockitoSugar import org.mockito.Mockito._ import org.junit.runner.RunWith import org.scalatest.junit.JUnitRunner trait Collaborator { def doSomething(t: => Thing) } trait Thing @RunWith(classOf[JUnitRunner]) class Test extends WordSpec with MockitoSugar { "The subject under test" should { "call the collaborator" in { // setup val m = mock[Collaborator] val t = mock[Thing] // test code: this would actually be invoked by the SUT m.doSomething(t) // verify the call verify(m).doSomething(t) } } } ``` I'm primarily interested in Mockito since that's what I'm using, but I'd be interested to see whether any of the major mock frameworks is capable of this kind of testing. The Test fails at runtime on the `verify` line, with an error like ``` Argument(s) are different! Wanted: collaborator.doSomething( ($anonfun$apply$3) <function> ); -> at Test$$anonfun$1$$anonfun$apply$1.apply(Test.scala:27) Actual invocation has different arguments: collaborator.doSomething( ($anonfun$apply$2) <function> ); -> at Test$$anonfun$1$$anonfun$apply$1.apply(Test.scala:24) ``` If I'm understanding the situation correctly, the compiler is implicitly wrapping `t` in a nullary function that returns `t`. The mock framework is then comparing that function to the one produced in the test code, which is equivalent but not `equals()`. My case is a relatively simple version of the problem, but I think this would be an issue with any higher-order function.

Original source