Mockito with Groovy fails to create stubs for partial mock for abstract class derivative

I am using Mockito 2.8.9 with Groovy 2.4.1 and JUnit 4.12 (openjdk version “1.8.0_131”)

The setup:

• I have an instance of the Failure class that is derived from abstract AbstractBase parent.

• I am stubbing partial mock (spy) using doXxx methods.

• => failure

• For contrast, the above steps are repeated with Success which is derived from regular Base parent.

• => success

The tests:

import org.junit.Test
import static org.mockito.Mockito.*

abstract class AbstractBase { }

class Failure extends AbstractBase {
    def method() { }
}

class Base { }

class Success extends Base {
    def method() { }
}

class FooTest {
    @Test
    void failed() {
        def sut = spy(new Failure())
        doReturn(1).when(sut).method()
    }

    @Test
    void succeed() {
        def sut = spy(new Success())
        doReturn(1).when(sut).method()
    }
}

As test names suggest, succeed() works as expected, while failed() generates an error with following message and stack trace (integer is incidental, I verified with several types):

org.mockito.exceptions.misusing.WrongTypeOfReturnValue: 
Integer cannot be returned by getMetaClass()
getMetaClass() should return MetaClass
***
If you're unsure why you're getting above error read on.
Due to the nature of the syntax above problem might occur because:
1. This exception *might* occur in wrongly written multi-threaded tests.
   Please refer to Mockito FAQ on limitations of concurrency testing.
2. A spy is stubbed using when(spy.foo()).then() syntax. It is safer to stub spies - 
   - with doReturn|Throw() family of methods. More in javadocs for Mockito.spy() method.


	at org.codehaus.groovy.runtime.callsite.CallSiteArray.createPogoSite(CallSiteArray.java:147)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.createCallSite(CallSiteArray.java:164)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:117)
	at FooTest.failed(FooTest.groovy:24)
	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 org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

Thank you!

P.S. I ran it also with Groovy 2.4.10, and with Mockito 2.7.22 – with the same result

[agabrys]

I found a working workaround. It requires some code changes, but only in tests. You can add the groovy.transform.CompileStatic annotation to the test class. I checked if for the above example.

Sources

package issue1108

abstract class DAO {}

package issue1108

class Person {}

package issue1108

class PersonDAO extends DAO {

	Person findById(Long id) {
		return new Person()
	}
}

Broken Test Class

package issue1108

import static org.junit.jupiter.api.Assertions.assertNotNull
import static org.mockito.Mockito.mock
import static org.mockito.Mockito.when

import org.junit.jupiter.api.Test
import org.mockito.Mockito

class PersonDAOTest extends DAO {

	@Test
	void fails() {
		def dao = mock(PersonDAO)
		when(dao.findById(Mockito.anyLong())).thenReturn(new Person())
		def person = dao.findById(1L)
		assertNotNull(person)
	}
}

org.mockito.exceptions.misusing.InvalidUseOfMatchersException: 
Invalid use of argument matchers!
0 matchers expected, 1 recorded:
-> at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)

This exception may occur if matchers are combined with raw values:
    //incorrect:
    someMethod(anyObject(), "raw String");
When using matchers, all arguments have to be provided by matchers.
For example:
    //correct:
    someMethod(anyObject(), eq("String by matcher"));

For more info see javadoc for Matchers class.

	at org.codehaus.groovy.runtime.callsite.CallSiteArray.createPogoSite(CallSiteArray.java:146)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.createCallSite(CallSiteArray.java:163)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:128)
	at issue1108.PersonDAOTest.fails(PersonDAOTest.groovy:15)
	[...]

Successful Test Class

package issue1108

import static org.junit.jupiter.api.Assertions.assertNotNull
import static org.mockito.Mockito.mock
import static org.mockito.Mockito.when

import groovy.transform.CompileStatic
import org.junit.jupiter.api.Test
import org.mockito.Mockito

@CompileStatic
class PersonDAOTest extends DAO {

	@Test
	void fails() {
		def dao = mock(PersonDAO)
		when(dao.findById(Mockito.anyLong())).thenReturn(new Person())
		def person = dao.findById(1L)
		assertNotNull(person)
	}
}

[solvingj]

We have a bunch of dynamic class loading happening, can’t use @CompileStatic at the moment. Any possibility of a different workaround?