Sporadic mock verification failures related to hashCode/equals on 3.12.1

Since updating from 3.11.2 to 3.12.0 (and getting similar errors on 3.12.1), I have seen some strange sometimes-reproducible verification failures on Mockito for tests which previously passed consistently.

I can’t yet establish a pattern or simple reproduction; it feels like it is somehow dependent on the order of test evaluation/usage with respect to other tests within the same JVM instance, and I have been unable to replicate locally.

There are two main classes I am seeing

1. mocks with interactions being tracked (and thus failing verifyNoInteractions(mock) after being put into HashSets (these did not seem to previously count as an interaction, and usually do not)

   com.thoughtworks.go.server.materials.postcommit.git.GitPostCommitHookImplementerTest > shouldReturnEmptyListIfParamHasNoValueForRepoURL() FAILED
       org.mockito.exceptions.verification.NoInteractionsWanted: 
       No interactions wanted here:
       -> at com.thoughtworks.go.server.materials.postcommit.git.GitPostCommitHookImplementerTest.shouldReturnEmptyListIfParamHasNoValueForRepoURL(GitPostCommitHookImplementerTest.java:93)
       But found this interaction on mock 'gitMaterial':
       -> at java.base/java.util.HashMap.hash(HashMap.java:340)
       Actually, above is the only interaction with this mock.
           at com.thoughtworks.go.server.materials.postcommit.git.GitPostCommitHookImplementerTest.shouldReturnEmptyListIfParamHasNoValueForRepoURL(GitPostCommitHookImplementerTest.java:93)
   

   https://github.com/gocd/gocd/blob/b7bba59201c857efc010c3493664802f218d2bae/server/src/test-fast/java/com/thoughtworks/go/server/materials/postcommit/git/GitPostCommitHookImplementerTest.java#L81-L94

2. mocks that are not considered equal to themselves when put inside a Collection and then searched for

   com.thoughtworks.go.server.materials.postcommit.git.GitPostCommitHookImplementerTest > shouldReturnListOfMaterialMatchingThePayloadURL() FAILED
       java.lang.AssertionError: 
       Expected: a collection containing <Mock for GitMaterial, hashCode: 0>
            but: was <Mock for GitMaterial, hashCode: 0>, was <Mock for GitMaterial, hashCode: 0>
           at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
           at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:8)
           at com.thoughtworks.go.server.materials.postcommit.git.GitPostCommitHookImplementerTest.shouldReturnListOfMaterialMatchingThePayloadURL(GitPostCommitHookImplementerTest.java:58)
   

   https://github.com/gocd/gocd/blob/b7bba59201c857efc010c3493664802f218d2bae/server/src/test-fast/java/com/thoughtworks/go/server/materials/postcommit/git/GitPostCommitHookImplementerTest.java#L41-L65

I have a handful of other examples too in different classes.

This could be confirmation bias, however since I saw some stuff was done with respect to hashCodes in #2331 I wondered if it could be related. Logging it here to see if anyone else has seen any similar weirdness or might know what is going on.

Environment

• Currently I cannot replicate locally (MacOS Big Sur w/AdoptOpenJDK 15.0.2) even where it is replicable on build/CI automation environment.
• The failures seem to be (somewhat) reproducible on AL2 Linux w/ Oracle JDK 15.0.1) but I cannot distinguish a pattern, and sometimes a different combination/ordering of tests does not seem to yield the same failure on exactly the same test code.

[vyazelenko]

@chadlwilson Correction. the changes in https://github.com/mockito/mockito/pull/2400 are not the root the breakage but the PR https://github.com/mockito/mockito/pull/2369 is. The https://github.com/mockito/mockito/pull/2402 reverted both, because https://github.com/mockito/mockito/pull/2400 is not needed if the https://github.com/mockito/mockito/pull/2369 is removed.

[TimvdLippe]

3.12.2 is currently being pushed to Maven Central and should be available in a couple of hours.