NullPointerException when calling methods on spy of a final class with JDK > 11

[JanMosigItemis]

Hi there,

I may have encountered a bug in mockito-inline with respect to spies of final classes. You may want to checkout this demo project: https://github.com/JanMosigItemis/mockito.inline.spy.bug

I have:

• Windows 10.0.19042.804
• Git Bash 2.30.0.windows.2
• Maven 3.6.3
• Surefire 3.0.0-M5
• Mockito-Inline 3.7.7
• JUnit 5.7.0
• -Dnet.bytebuddy.experimental=true
• mock-maker-inline

The following test runs into an NPE:

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

import java.lang.reflect.Method;

/**
 * Unit test for simple App.
 */
public class AppTest {
    @Test
    public void test_something() throws Exception {
        Method realMethod = getClass().getMethod("some_method");
        Method spyMethod = Mockito.spy(realMethod);
        spyMethod.invoke(this); // <- NPE
    }

    public void some_method() {

    }
}

I cannot pin point the exact cause of the NPE from the logs / stack traces. The NPE only happens when running a maven build with JDK >11. I tested with JDK12 and 15 (same result for both). However, the test runs successfully with JDK 11. Using a mock instead of a spy works on all JDKs.

Also running the test from within Eclipse (4.18.0) works when running Eclipse with JDK11 and does not work when running with JDK > 11.

Stacktrace is like this:

java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at java.base/jdk.internal.reflect.Reflection.verifyMemberAccess(Reflection.java:127)
	at java.base/java.lang.reflect.AccessibleObject.slowVerifyAccess(AccessibleObject.java:734)
	at java.base/java.lang.reflect.AccessibleObject.verifyAccess(AccessibleObject.java:720)
	at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:692)
	at java.base/java.lang.reflect.Method.invoke(Method.java:556)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:554)
	at de.itemis.mosig.mockito.inline.spy.bug.AppTest.test_something(AppTest.java:16)

Any thoughts on this?

[TimvdLippe]

java.lang.reflect.Method is one of the building blocks of Mockito and therefore we can't guarantee correctness when mocking/spying such classes. Instead, we recommend using real objects. For more information, please see the full discussion in #2026 (comment) This will likely be addressed in #1833 to notify users when they run into these kind of situations.

[JanMosigItemis]

Thank you very much. I did not know that creating a spy will change the behavior of all instances of that type.