Capturing method references with mockito

Question

I'm trying to mock a collaborator, named Worker and capture arguments of its method execute which runs in different thread. However, the method itself has method references as arguments: childService::listClients and childService::refreshObjects. When I assert method references with captured arguments, I get different lambda objects.

Is there a way to reach and assert them in proper way?

The class being tested:

public class ParentService {
    private ChildService childService;
    private Worker worker;
    ...
    public void doAction() {
        worker.execute(
                childService::listClients,
                childService::refreshObjects
        );
    }
}

The test:

@Test
public void shouldUseChildService() {
    ArgumentCaptor<Callable> callableCaptor = ArgumentCaptor.forClass(Callable.class);
    ArgumentCaptor<Consumer> consumerCaptor = ArgumentCaptor.forClass(Consumer.class);

    parentService.doAction();

    verify(worker).execute(callableCaptor.capture(), consumerCaptor.capture());
    assertEquals((Callable) childService::listClients, callableCaptor.getValue());
    assertEquals((Consumer) childService::refreshObjects, consumerCaptor.getValue());
}

Assertion error:

    java.lang.AssertionError: 
    Expected :org.app.services.ParentServiceTest$$Lambda$4/990416209@1786dec2
    Actual   :org.app.services.ParentServiceTest$$Lambda$1/1340328248@74650e52
at org.junit.Assert.failNotEquals(Assert.java:743)
    at org.junit.Assert.assertEquals(Assert.java:118)
    at org.junit.Assert.assertEquals(Assert.java:144)
    at org.app.services.ParentServiceTest.shouldUseChildService(ParenServiceTest.java:66)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37)
    at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:78)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:212)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:68)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)

Answer 1

First Mock your Worker with Mockito (just as you did). Also mock your ChildService. Then:

@Test
public void shouldUseChildService() {
  ArgumentCaptor<Callable> callableCaptor = ArgumentCaptor.forClass(Callable.class);
  ArgumentCaptor<Consumer> consumerCaptor = ArgumentCaptor.forClass(Consumer.class);

  parentService.doAction();

  verify(worker).execute(callableCaptor.capture(), consumerCaptor.capture());
  callableCaptor.getValue().call(); //this will execute whatever was captured
  consumerCaptor.getValue().accept(null);//this will execute whatever was captured

  // now verify that childService::listClients and childService::refreshObjects have been called
}