Sporadic java.lang.AssertionError in MockUtil.getMockHandlerOrNull

[XN137]

hello,

we are using mockito 4.8.1 on jdk 11 targeting java 8

recently one of our maven modules added a dependency to mockito-inline in order to mock final classes/methods (normally modules use normal mockito)

we started seeing sporadically failing tests around this:

java.lang.AssertionError
	at org.mockito.internal.util.MockUtil.getMockHandlerOrNull(MockUtil.java:160)
	at org.mockito.internal.util.MockUtil.getMockHandler(MockUtil.java:115)
	at org.mockito.internal.stubbing.answers.InvocationInfo.isVoid(InvocationInfo.java:94)
	at org.mockito.internal.stubbing.answers.Returns.validateFor(Returns.java:34)
	at org.mockito.internal.stubbing.InvocationContainerImpl.addAnswer(InvocationContainerImpl.java:65)
	at org.mockito.internal.stubbing.InvocationContainerImpl.addAnswer(InvocationContainerImpl.java:56)
	at org.mockito.internal.stubbing.OngoingStubbingImpl.thenAnswer(OngoingStubbingImpl.java:32)
	at org.mockito.internal.stubbing.BaseStubbing.thenReturn(BaseStubbing.java:34)
        (..)

also:

java.lang.AssertionError
	at org.mockito.internal.util.MockUtil.getMockHandlerOrNull(MockUtil.java:160)
	at org.mockito.internal.util.MockUtil.isMock(MockUtil.java:147)
	at org.mockito.internal.stubbing.StubberImpl.when(StubberImpl.java:43)
        (..)

for the latter error the test code looks like this:

import com.azure.resourcemanager.AzureResourceManager;
import com.azure.resourcemanager.compute.models.GalleryImageVersions;

(..)
  @Test
  public void testMethod() {
    AzureResourceManager mockArmClient = mock(AzureResourceManager.class);  // final class
    GalleryImageVersions mockGalleryImageVersions = mock(GalleryImageVersions.class); // interface
    doReturn(mockGalleryImageVersions).when(mockArmClient).galleryImageVersions();
    doReturn(null).when(mockGalleryImageVersions).listByGalleryImage(anyString(), anyString(), anyString()); <- assertion fails here
    (..)
  }

additional notes:

• these tests are not failing every time and the number of failing tests varies (but all with assertion error in MockUtil.getMockHandlerOrNull)
• in case it is relevant: it could be that the maven module depends on both <artifactId>mockito-inline</artifactId> and <artifactId>mockito-core</artifactId> but these tests are not using multiple classloaders or the like

are we doing anything wrong or is this a mockito bug?

the failing assertion has only recently been added in 4.8.0 for supporting the mockmaker settings:
https://github.com/mockito/mockito/blame/3faa00299a8c0793cf17ce072229f2e8ffea4579/src/main/java/org/mockito/internal/util/MockUtil.java#L160
any ideas when this can resolve to different mock makers?

[TimvdLippe]

Thanks for filing the issue. Could you please provide us a minimal reproduction case that we can clone/download to debug the issue? Thanks in advance!

[XN137]

the full code is from a large private codebase, so i tried to distill it down to a minimal public example however now the error does not occur anymore with the mentioned code... (was running the test in a loop in 4 shells).

do you have any remote idea when this assertion might be failing?
when does mockMakers.values() return more than 1 element?
could it be related to classloader shenanigans maybe (i.e. Thread.currentThread().getContextClassLoader()) ?

[TimvdLippe]

Seems like this is a similar issue to #2823 In your large codebase, it is likely that you have clashing usages of mockmakers, triggering this assertion. Hopefully that additional information can help you further debug this issue.