jeffkbkim commented on code in PR #14017:
URL: https://github.com/apache/kafka/pull/14017#discussion_r1270946493


##########
group-coordinator/src/test/java/org/apache/kafka/coordinator/group/GroupMetadataManagerTest.java:
##########
@@ -5524,5 +5670,2897 @@ private static Record newGroupMetadataRecord(
             )
         );
     }
+
+    @Test
+    public void testNewMemberTimeoutCompletion() throws Exception {
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        JoinGroupRequestData joinRequest = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withMemberId(UNKNOWN_MEMBER_ID)
+            .withDefaultProtocolTypeAndProtocols()
+            .withSessionTimeoutMs(context.genericGroupNewMemberJoinTimeoutMs + 
5000)
+            .build();
+
+        CompletableFuture<JoinGroupResponseData> joinFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> result = 
context.sendGenericGroupJoin(joinRequest, joinFuture);
+        assertTrue(result.records().isEmpty());
+        assertFalse(joinFuture.isDone());
+
+        
context.sleepAndAssertEmptyResult(context.genericGroupInitialRebalanceDelayMs);
+
+        assertTrue(joinFuture.isDone());
+        assertEquals(Errors.NONE.code(), joinFuture.get().errorCode());
+
+        assertEquals(0, 
group.allMembers().stream().filter(GenericGroupMember::isNew).count());
+
+        SyncGroupRequestData syncRequest = new SyncGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withMemberId(joinFuture.get().memberId())
+            .withGenerationId(joinFuture.get().generationId())
+            .build();
+
+        CompletableFuture<SyncGroupResponseData> syncFuture = new 
CompletableFuture<>();
+        result = context.sendGenericGroupSync(syncRequest, syncFuture);
+
+        assertEquals(
+            Collections.singletonList(newGroupMetadataRecord(group, 
MetadataVersion.latest())),
+            result.records()
+        );
+        // Simulate a successful write to the log.
+        result.appendFuture().complete(null);
+
+        assertTrue(syncFuture.isDone());
+        assertEquals(Errors.NONE.code(), syncFuture.get().errorCode());
+        assertEquals(1, group.size());
+
+        // Make sure the NewMemberTimeout is not still in effect, and the 
member is not kicked
+        
context.sleepAndAssertEmptyResult(context.genericGroupNewMemberJoinTimeoutMs);
+        assertEquals(1, group.size());
+
+        // Member should be removed as heartbeat expires.
+        List<ExpiredTimeout<Void, Record>> timeouts = context.sleep(5000);
+        List<Record> expectedRecords = 
Collections.singletonList(newGroupMetadataRecord("group-id",
+                new GroupMetadataValue()
+                    .setMembers(Collections.emptyList())
+                    .setGeneration(2)
+                    .setLeader(null)
+                    .setProtocolType("consumer")
+                    .setProtocol(null)
+                    .setCurrentStateTimestamp(context.time.milliseconds()),
+                MetadataVersion.latest()));
+
+        assertEquals(1, timeouts.size());
+        String memberId = joinFuture.get().memberId();
+        timeouts.forEach(timeout -> {
+            assertEquals(genericGroupHeartbeatKey("group-id", memberId), 
timeout.key);
+            assertEquals(expectedRecords, timeout.result.records());
+        });
+
+        assertEquals(0, group.size());
+    }
+
+    @Test
+    public void testNewMemberFailureAfterJoinGroupCompletion() throws 
Exception {
+        // For old versions of the JoinGroup protocol, new members were subject
+        // to expiration if the rebalance took long enough. This test case 
ensures
+        // that following completion of the JoinGroup phase, new members follow
+        // normal heartbeat expiration logic.
+
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        JoinGroupRequestData joinRequest = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withMemberId(UNKNOWN_MEMBER_ID)
+            .withDefaultProtocolTypeAndProtocols()
+            .withSessionTimeoutMs(5000)
+            .withRebalanceTimeoutMs(10000)
+            .build();
+
+        JoinGroupResponseData joinResponse = 
context.joinGenericGroupAndCompleteJoin(joinRequest, false, false);
+        assertEquals(Errors.NONE.code(), joinResponse.errorCode());
+
+        String memberId = joinResponse.memberId();
+        assertEquals(memberId, joinResponse.leader());
+        assertEquals(1, joinResponse.generationId());
+
+        SyncGroupRequestData syncRequest = new SyncGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withMemberId(memberId)
+            .withGenerationId(1)
+            .build();
+
+        CompletableFuture<SyncGroupResponseData> syncResponseFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> result = 
context.sendGenericGroupSync(syncRequest, syncResponseFuture);
+
+        assertEquals(
+            Collections.singletonList(newGroupMetadataRecord(group, 
MetadataVersion.latest())),
+            result.records()
+        );
+        // Simulate a successful write to the log.
+        result.appendFuture().complete(null);
+
+        assertTrue(syncResponseFuture.isDone());
+        assertEquals(Errors.NONE.code(), syncResponseFuture.get().errorCode());
+
+        assertTrue(group.isInState(STABLE));
+        assertEquals(1, group.generationId());
+
+        CompletableFuture<JoinGroupResponseData> otherJoinFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> otherJoinResult = 
context.sendGenericGroupJoin(
+            joinRequest.setMemberId(UNKNOWN_MEMBER_ID),
+            otherJoinFuture);
+
+        CompletableFuture<JoinGroupResponseData> joinFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> joinResult = 
context.sendGenericGroupJoin(
+            joinRequest.setMemberId(memberId),
+            joinFuture);
+
+        assertTrue(otherJoinResult.records().isEmpty());
+        assertTrue(joinResult.records().isEmpty());
+        assertTrue(joinFuture.isDone());
+        assertTrue(otherJoinFuture.isDone());
+
+        verifySessionExpiration(context, group, 5000);
+    }
+
+    @Test
+    public void testStaticMemberFenceDuplicateRejoinedFollower() throws 
Exception {
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        RebalanceResult rebalanceResult = staticMembersJoinAndRebalance(
+            context,
+            "group-id",
+            "leader-instance-id",
+            "follower-instance-id"
+        );
+
+        // A third member joins. Trigger a rebalance.
+        JoinGroupRequestData request = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withMemberId(UNKNOWN_MEMBER_ID)
+            .withDefaultProtocolTypeAndProtocols()
+            .build();
+
+        context.sendGenericGroupJoin(request, new CompletableFuture<>());
+
+        assertTrue(group.isInState(PREPARING_REBALANCE));
+
+        // Old follower rejoins group will be matching current member.id.
+        CompletableFuture<JoinGroupResponseData> oldFollowerJoinFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> result = context.sendGenericGroupJoin(
+            request
+                .setMemberId(rebalanceResult.followerId)
+                .setGroupInstanceId("follower-instance-id"),
+            oldFollowerJoinFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertFalse(oldFollowerJoinFuture.isDone());
+
+        // Duplicate follower joins group with unknown member id will trigger 
member id replacement.
+        result = context.sendGenericGroupJoin(
+            
request.setMemberId(UNKNOWN_MEMBER_ID).setGroupInstanceId("follower-instance-id"),
+            new CompletableFuture<>());
+
+        // Old member shall be fenced immediately upon duplicate follower 
joins.
+        assertTrue(result.records().isEmpty());
+        assertTrue(oldFollowerJoinFuture.isDone());
+
+        JoinGroupResponseData expectedResponse = new JoinGroupResponseData()
+            .setErrorCode(Errors.FENCED_INSTANCE_ID.code())
+            .setProtocolName(null)
+            .setProtocolType(null)
+            .setLeader(UNKNOWN_MEMBER_ID)
+            .setMemberId(rebalanceResult.followerId)
+            .setGenerationId(-1);
+
+        checkJoinGroupResponse(
+            expectedResponse,
+            oldFollowerJoinFuture.get(),
+            group,
+            PREPARING_REBALANCE,
+            Collections.emptySet()
+        );
+    }
+
+    @Test
+    public void 
testStaticMemberFenceDuplicateSyncingFollowerAfterMemberIdChanged() throws 
Exception {
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        RebalanceResult rebalanceResult = staticMembersJoinAndRebalance(
+            context,
+            "group-id",
+            "leader-instance-id",
+            "follower-instance-id"
+        );
+
+        // Known leader rejoins will trigger rebalance.
+        JoinGroupRequestData request = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withGroupInstanceId("leader-instance-id")
+            .withMemberId(rebalanceResult.leaderId)
+            .withDefaultProtocolTypeAndProtocols()
+            .withRebalanceTimeoutMs(10000)
+            .build();
+
+        CompletableFuture<JoinGroupResponseData> leaderJoinFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> result = 
context.sendGenericGroupJoin(request, leaderJoinFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertFalse(leaderJoinFuture.isDone());
+        assertTrue(group.isInState(PREPARING_REBALANCE));
+
+        // Old follower rejoins group will match current member.id.
+        CompletableFuture<JoinGroupResponseData> oldFollowerJoinFuture = new 
CompletableFuture<>();
+        result = context.sendGenericGroupJoin(
+                
request.setMemberId(rebalanceResult.followerId).setGroupInstanceId("follower-instance-id"),
+                oldFollowerJoinFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertTrue(oldFollowerJoinFuture.isDone());
+        assertTrue(leaderJoinFuture.isDone());
+
+        JoinGroupResponseData expectedLeaderResponse = new 
JoinGroupResponseData()
+            .setErrorCode(Errors.NONE.code())
+            .setGenerationId(rebalanceResult.generationId + 1)
+            .setMemberId(rebalanceResult.leaderId)
+            .setLeader(rebalanceResult.leaderId)
+            .setProtocolName("range")
+            .setProtocolType("consumer")
+            .setMembers(toJoinResponseMembers(group));
+
+        Set<String> expectedGroupInstanceIds = new HashSet<>();
+        expectedGroupInstanceIds.add("leader-instance-id");
+        expectedGroupInstanceIds.add("follower-instance-id");
+
+        checkJoinGroupResponse(
+            expectedLeaderResponse,
+            leaderJoinFuture.get(),
+            group,
+            COMPLETING_REBALANCE,
+            expectedGroupInstanceIds
+        );
+
+        assertEquals(rebalanceResult.leaderId, 
leaderJoinFuture.get().memberId());
+        assertEquals(rebalanceResult.leaderId, 
leaderJoinFuture.get().leader());
+
+        // Old follower should get a successful join group response.
+        assertTrue(oldFollowerJoinFuture.isDone());
+
+        JoinGroupResponseData expectedFollowerResponse = new 
JoinGroupResponseData()
+            .setErrorCode(Errors.NONE.code())
+            .setGenerationId(rebalanceResult.generationId + 1)
+            .setMemberId(oldFollowerJoinFuture.get().memberId())
+            .setLeader(rebalanceResult.leaderId)
+            .setProtocolName("range")
+            .setProtocolType("consumer");
+
+        checkJoinGroupResponse(
+            expectedFollowerResponse,
+            oldFollowerJoinFuture.get(),
+            group,
+            COMPLETING_REBALANCE,
+            Collections.emptySet()
+        );
+
+        assertTrue(group.isInState(COMPLETING_REBALANCE));
+        assertEquals(rebalanceResult.followerId, 
oldFollowerJoinFuture.get().memberId());
+        assertEquals(rebalanceResult.leaderId, 
oldFollowerJoinFuture.get().leader());
+
+        // Duplicate follower joins group with unknown member id will trigger 
member.id replacement,
+        // and will also trigger a rebalance under CompletingRebalance state; 
the old follower sync callback
+        // will return fenced exception while broker replaces the member 
identity with the duplicate follower joins.
+        SyncGroupRequestData syncRequest = new SyncGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withGroupInstanceId("follower-instance-id")
+            .withGenerationId(oldFollowerJoinFuture.get().generationId())
+            .withMemberId(oldFollowerJoinFuture.get().memberId())
+            .build();
+
+        CompletableFuture<SyncGroupResponseData> oldFollowerSyncFuture = new 
CompletableFuture<>();
+        result = context.sendGenericGroupSync(syncRequest, 
oldFollowerSyncFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertFalse(oldFollowerSyncFuture.isDone());
+
+        CompletableFuture<JoinGroupResponseData> duplicateFollowerJoinFuture = 
new CompletableFuture<>();
+        result = context.sendGenericGroupJoin(
+            
request.setMemberId(UNKNOWN_MEMBER_ID).setGroupInstanceId("follower-instance-id"),
+            duplicateFollowerJoinFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertTrue(group.isInState(PREPARING_REBALANCE));
+        assertFalse(duplicateFollowerJoinFuture.isDone());
+        assertTrue(oldFollowerSyncFuture.isDone());
+        assertEquals(Errors.FENCED_INSTANCE_ID.code(), 
oldFollowerSyncFuture.get().errorCode());
+
+        // Advance clock by rebalance timeout so that the join phase completes 
with duplicate follower.
+        // Leader is kicked out.
+        context.sleepAndAssertEmptyResult(10000);
+
+        assertTrue(duplicateFollowerJoinFuture.isDone());
+        assertTrue(group.isInState(COMPLETING_REBALANCE));
+        assertEquals(3, group.generationId());
+        assertEquals(1, group.size());
+        
assertTrue(group.hasMemberId(duplicateFollowerJoinFuture.get().memberId()));
+        assertEquals(duplicateFollowerJoinFuture.get().memberId(), 
duplicateFollowerJoinFuture.get().leader());
+    }
+
+    @Test
+    public void 
testStaticMemberFenceDuplicateRejoiningFollowerAfterMemberIdChanged() throws 
Exception {
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        RebalanceResult rebalanceResult = staticMembersJoinAndRebalance(
+            context,
+            "group-id",
+            "leader-instance-id",
+            "follower-instance-id"
+        );
+
+        // Known leader rejoins will trigger rebalance.
+        JoinGroupRequestData request = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withGroupInstanceId("leader-instance-id")
+            .withMemberId(rebalanceResult.leaderId)
+            .withDefaultProtocolTypeAndProtocols()
+            .withRebalanceTimeoutMs(10000)
+            .build();
+
+        CompletableFuture<JoinGroupResponseData> leaderJoinFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> result = 
context.sendGenericGroupJoin(request, leaderJoinFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertFalse(leaderJoinFuture.isDone());
+        assertTrue(group.isInState(PREPARING_REBALANCE));
+
+        // Duplicate follower joins group will trigger member id replacement.
+        CompletableFuture<JoinGroupResponseData> duplicateFollowerJoinFuture = 
new CompletableFuture<>();
+        result = context.sendGenericGroupJoin(
+            
request.setMemberId(UNKNOWN_MEMBER_ID).setGroupInstanceId("follower-instance-id"),
+            duplicateFollowerJoinFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertTrue(duplicateFollowerJoinFuture.isDone());
+
+        // Old follower rejoins group will fail because member id is already 
updated.
+        CompletableFuture<JoinGroupResponseData> oldFollowerJoinFuture = new 
CompletableFuture<>();
+        result = context.sendGenericGroupJoin(
+            request.setMemberId(rebalanceResult.followerId),
+            oldFollowerJoinFuture);
+
+        assertTrue(result.records().isEmpty());
+        assertTrue(oldFollowerJoinFuture.isDone());
+        assertTrue(leaderJoinFuture.isDone());
+
+        JoinGroupResponseData expectedLeaderResponse = new 
JoinGroupResponseData()
+            .setErrorCode(Errors.NONE.code())
+            .setGenerationId(rebalanceResult.generationId + 1)
+            .setMemberId(rebalanceResult.leaderId)
+            .setLeader(rebalanceResult.leaderId)
+            .setProtocolName("range")
+            .setProtocolType("consumer")
+            .setMembers(toJoinResponseMembers(group));
+
+        Set<String> expectedGroupInstanceIds = new HashSet<>();
+        expectedGroupInstanceIds.add("leader-instance-id");
+        expectedGroupInstanceIds.add("follower-instance-id");
+
+        checkJoinGroupResponse(
+            expectedLeaderResponse,
+            leaderJoinFuture.get(),
+            group,
+            COMPLETING_REBALANCE,
+            expectedGroupInstanceIds
+        );
+
+        assertTrue(duplicateFollowerJoinFuture.isDone());
+
+        JoinGroupResponseData expectedDuplicateFollowerResponse = new 
JoinGroupResponseData()
+            .setErrorCode(Errors.NONE.code())
+            .setGenerationId(rebalanceResult.generationId + 1)
+            .setMemberId(duplicateFollowerJoinFuture.get().memberId())
+            .setLeader(rebalanceResult.leaderId)
+            .setProtocolName("range")
+            .setProtocolType("consumer")
+            .setMembers(Collections.emptyList());
+
+        checkJoinGroupResponse(
+            expectedDuplicateFollowerResponse,
+            duplicateFollowerJoinFuture.get(),
+            group,
+            COMPLETING_REBALANCE,
+            Collections.emptySet()
+        );
+
+        assertTrue(duplicateFollowerJoinFuture.isDone());
+
+        JoinGroupResponseData expectedOldFollowerResponse = new 
JoinGroupResponseData()
+            .setErrorCode(Errors.FENCED_INSTANCE_ID.code())
+            .setGenerationId(-1)
+            .setMemberId(rebalanceResult.followerId)
+            .setLeader(UNKNOWN_MEMBER_ID)
+            .setProtocolName(null)
+            .setProtocolType(null)
+            .setMembers(Collections.emptyList());
+
+        checkJoinGroupResponse(
+            expectedOldFollowerResponse,
+            oldFollowerJoinFuture.get(),
+            group,
+            COMPLETING_REBALANCE,
+            Collections.emptySet()
+        );
+    }
+
+    @Test
+    public void testStaticMemberRejoinWithKnownMemberId() throws Exception {
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        JoinGroupRequestData request = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withMemberId(UNKNOWN_MEMBER_ID)
+            .withGroupInstanceId("group-instance-id")
+            .withDefaultProtocolTypeAndProtocols()
+            .build();
+
+        JoinGroupResponseData joinResponse = 
context.joinGenericGroupAndCompleteJoin(request, false, false);
+        assertEquals(Errors.NONE.code(), joinResponse.errorCode());
+
+        String memberId = joinResponse.memberId();
+
+        CompletableFuture<JoinGroupResponseData> rejoinResponseFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> result = context.sendGenericGroupJoin(
+            request.setMemberId(memberId),
+            rejoinResponseFuture);
+
+        // The second join group should return immediately since we are using 
the same metadata during CompletingRebalance.
+        assertTrue(result.records().isEmpty());
+        assertTrue(group.isInState(COMPLETING_REBALANCE));
+        assertTrue(rejoinResponseFuture.isDone());
+        assertEquals(Errors.NONE.code(), 
rejoinResponseFuture.get().errorCode());
+
+        SyncGroupRequestData syncRequest = new SyncGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withMemberId(memberId)
+            .withGenerationId(joinResponse.generationId())
+            .withGroupInstanceId("group-instance-id")
+            .build();
+
+        CompletableFuture<SyncGroupResponseData> syncFuture = new 
CompletableFuture<>();
+        result = context.sendGenericGroupSync(syncRequest, syncFuture);
+
+        assertEquals(
+            Collections.singletonList(newGroupMetadataRecord(group, 
MetadataVersion.latest())),
+            result.records()
+        );
+        // Successful write to the log.
+        result.appendFuture().complete(null);
+
+        assertTrue(syncFuture.isDone());
+        assertEquals(Errors.NONE.code(), syncFuture.get().errorCode());
+        assertTrue(group.isInState(STABLE));
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {true, false})
+    public void testStaticMemberRejoinWithLeaderIdAndUnknownMemberId(
+        boolean supportSkippingAssignment
+    ) throws Exception {
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        RebalanceResult rebalanceResult = staticMembersJoinAndRebalance(
+            context,
+            "group-id",
+            "leader-instance-id",
+            "follower-instance-id"
+        );
+
+        // A static leader rejoin with unknown id will not trigger rebalance, 
and no assignment will be returned.
+        // As the group was in Stable state and the member id was updated, 
this will generate records.
+        JoinGroupRequestData joinRequest = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withGroupInstanceId("leader-instance-id")
+            .withMemberId(UNKNOWN_MEMBER_ID)
+            .withDefaultProtocolTypeAndProtocols()
+            .build();
+
+        CompletableFuture<JoinGroupResponseData> joinResponseFuture = new 
CompletableFuture<>();
+        CoordinatorResult<Void, Record> result = context.sendGenericGroupJoin(
+            joinRequest,
+            joinResponseFuture,
+            true,
+            supportSkippingAssignment);
+
+        assertEquals(
+            Collections.singletonList(newGroupMetadataRecord(group, 
MetadataVersion.latest())),
+            result.records()
+        );
+        // Simulate a successful write to the log.
+        result.appendFuture().complete(null);
+        assertTrue(joinResponseFuture.isDone());
+
+        Set<String> expectedGroupInstanceIds = new HashSet<>();
+        expectedGroupInstanceIds.add("leader-instance-id");
+        expectedGroupInstanceIds.add("follower-instance-id");
+
+        String leader = supportSkippingAssignment ?
+            joinResponseFuture.get().memberId() : rebalanceResult.leaderId;
+
+        List<JoinGroupResponseMember> members = supportSkippingAssignment ?
+            toJoinResponseMembers(group) : Collections.emptyList();
+
+        JoinGroupResponseData expectedJoinResponse = new 
JoinGroupResponseData()
+            .setErrorCode(Errors.NONE.code())
+            .setGenerationId(rebalanceResult.generationId)
+            .setMemberId(joinResponseFuture.get().memberId())
+            .setLeader(leader)
+            .setProtocolName("range")
+            .setProtocolType("consumer")
+            .setSkipAssignment(supportSkippingAssignment)
+            .setMembers(members);
+
+        checkJoinGroupResponse(
+            expectedJoinResponse,
+            joinResponseFuture.get(),
+            group,
+            STABLE,
+            supportSkippingAssignment ? expectedGroupInstanceIds : 
Collections.emptySet()
+        );
+    }
+
+    @Test
+    public void testStaticMemberRejoinWithLeaderIdAndKnownMemberId() throws 
Exception {
+        GroupMetadataManagerTestContext context = new 
GroupMetadataManagerTestContext.Builder()
+            .build();
+        GenericGroup group = context.createGenericGroup("group-id");
+
+        RebalanceResult rebalanceResult = staticMembersJoinAndRebalance(
+            context,
+            "group-id",
+            "leader-instance-id",
+            "follower-instance-id"
+        );
+
+        // Known static leader rejoin will trigger rebalance.
+        JoinGroupRequestData request = new JoinGroupRequestBuilder()
+            .withGroupId("group-id")
+            .withGroupInstanceId("leader-instance-id")
+            .withMemberId(rebalanceResult.leaderId)
+            .withDefaultProtocolTypeAndProtocols()
+            .withRebalanceTimeoutMs(10000)
+            .build();
+
+        JoinGroupResponseData joinResponse = 
context.joinGenericGroupAndCompleteJoin(request, true, true, 10000);
+

Review Comment:
   added. thanks for the catch



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