mockito-kotlin cannot verify higher-order functions in Robolectric Tests

@nhaarman , the area that I was trying to test was like this

val testArg = mock<(String) -> Unit>()
val result = someClass.doSomething(testArg)
verify(testArg).invoke(any())

And the error comes out as the folllwing

org.mockito.exceptions.misusing.UnfinishedVerificationException: 
Missing method call for verify(mock) here:
-> at com.nhaarman.mockitokotlin2.VerificationKt.verify(Verification.kt:42)

Example of correct verification:
    verify(mock).doSomething()

Also, this error might show up because you verify either of: final/private/equals()/hashCode() methods.
Those methods *cannot* be stubbed/verified.
Mocking methods declared on non-public parent classes is not supported.

	at org.mockito.internal.junit.JUnitRule$1.evaluate(JUnitRule.java:44)
	at com.hootsuite.testing.rule.RxJavaSchedulerRule$apply$1.evaluate(RxJavaSchedulerRule.kt:31)
	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
	at org.robolectric.internal.SandboxTestRunner$2.evaluate(SandboxTestRunner.java:253)
	at org.robolectric.internal.SandboxTestRunner.runChild(SandboxTestRunner.java:130)
	at org.robolectric.internal.SandboxTestRunner.runChild(SandboxTestRunner.java:42)
...
com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)

[jachenry]

We’re seeing the same issue in our project. Our workaround is to create a test only interface that satisfies the higher-order function and can be verified. Using your example it’d look like:

val testCallback = mock<Callback>()
val result = someClass.doSomething(testCallback::invoke)
verify(testCallback).invoke(any())

interface Callback {
  operator fun invoke(value: String)
}

Less than ideal but the only workaround we’ve found. Please let me know if there is an easier way.

[jenzz]

@jachenry @davidxiasc

Simply declaring a private interface Callback : () -> Unit is sufficient as a workaround.