Hello,

The following test passes with Groovy 2.4 and 2.5, and fails with Groovy 3.0 (with Mockito 3.7.7 and JUnit 4.13.1 in all cases):

import org.junit.Test
import org.junit.runner.RunWith
import org.mockito.InjectMocks
import org.mockito.Mock
import org.mockito.junit.MockitoJUnitRunner

import static org.mockito.Mockito.verify

@RunWith(MockitoJUnitRunner)
class GroovyMockitoTest {
    static class Helper {
        void helper() { }
    }

    static class Service {
        private final Helper helper

        Service(Helper helper) {
            this.helper = helper
        }

        void service() {
            helper.helper()
        }
    }

    @Mock Helper helper
    @InjectMocks Service service

    @Test
    void testService() {
        service.service()
        verify(helper).helper()
    }
}

The actual error:

java.lang.NullPointerException
	at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:38)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:130)
	at GroovyMockitoTest$Service.service(GroovyMockitoTest.groovy:24)
	at GroovyMockitoTest$Service$service.call(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:130)
	at GroovyMockitoTest.testService(GroovyMockitoTest.groovy:33)
	[... junit ...]

I guess this is like #72, where getMetaClass() is not ignored and returns null.

I think the difference is that in Groovy 3.0, internal methods such as getMetaClass() are no longer marked synthetic: GROOVY-8495. Now they are @groovy.transform.Generated and @groovy.transform.Internal.

As far as I can tell, Mockito works with Groovy 2.4/2.5 only because ByteBuddy ignores synthetic methods. I see the existing ignoreAlso(isGroovyMethod()) but as far as I can tell, it has no effect with current versions of Groovy. (I assume it did in the past.)

I think that the fix is to ignore methods annotated with @groovy.transform.Internal. I don't know whether that should be done in Mockito or in ByteBuddy. Please let me know if I should report it somewhere else, or if you'd like me to ask the Groovy developers for their input.

Thank you for working on Mockito!