Mockito 2 mock-maker-inline not able to mock Object methods on an interface

Hi there,

I recently upgraded from Mockito 1.9.5 to 2.7.22 (mockito-inline), and some tests started failed as Mockito is unable to mock Object.toString() method on an interface.

It appears to be that the inline mock maker cannot mock Object methods on an interface, using a class (HashSet for the below example) or mockito-core instead of mockito-inline makes it work.

System:

OS:       Windows 10 (version 1703)
Java:     JDK 1.8u131
Mockito:  org.mockito:mockito-inline:2.7.22 //org.mockito:mockito-core:2.7.22 works fine!
Junit:    junit:junit:4.12

Sample example that fails:

import org.junit.Assert;
import org.junit.Test;
import org.mockito.Mockito;
import java.util.Set;

public class TestInterfaceToString {
    @Test
    public void testInterfaceToString() {
        Set set = Mockito.mock(Set.class); // Change Set.class to HashSet.class makes it work
        Mockito.when(set.toString()).thenReturn("bla");
        Assert.assertEquals("bla", set.toString());
    }
}

Output:

"C:\Program Files\Java\jdk1.8.0_131\bin\java" -Didea.test.cyclic.buffer.size=1048576 "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2017.1.2\lib\idea_rt.jar=58071:C:\Program Files\JetBrains\IntelliJ IDEA 2017.1.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\JetBrains\IntelliJ IDEA 2017.1.2\lib\idea_rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2017.1.2\plugins\junit\lib\junit-rt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;C:\Users\Mina\Documents\IdeaProjects\TestingMockito2\out\production\TestingMockito2;C:\Users\Mina\.m2\repository\org\mockito\mockito-inline\2.7.22\mockito-inline-2.7.22.jar;C:\Users\Mina\.m2\repository\org\mockito\mockito-core\2.7.22\mockito-core-2.7.22.jar;C:\Users\Mina\.m2\repository\net\bytebuddy\byte-buddy\1.6.11\byte-buddy-1.6.11.jar;C:\Users\Mina\.m2\repository\net\bytebuddy\byte-buddy-agent\1.6.11\byte-buddy-agent-1.6.11.jar;C:\Users\Mina\.m2\repository\org\objenesis\objenesis\2.5\objenesis-2.5.jar;C:\Users\Mina\.m2\repository\junit\junit\4.12\junit-4.12.jar;C:\Users\Mina\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 TestInterfaceToString

org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
   Those methods *cannot* be stubbed/verified.
   Mocking methods declared on non-public parent classes is not supported.
2. inside when() you don't call method on mock but on some other object.

	at TestInterfaceToString.setUp(TestInterfaceToString.java:20)
	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:497)
	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.RunBefores.evaluate(RunBefores.java:24)
	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)

Process finished with exit code -1

Cheers, Mina

[TimvdLippe]

@johnjohndoe There is not a minium JDK version for Mockito, but there are a small subset of errors that are JDK related and fixed in more recent versions. I think all versions > 1.8.45 are good enough for this subset.

[raphw]

Yes, its a bug in the inline mock maker. Fixed in attached PR.