fix(dm): resolve flaky TestWorker panic on unexpected Resume() call

[Copilot]

TestWorker intermittently panicked when checkAndAutoResume dispatched an unexpected Resume() call on the mock before the test registered that expectation.

Root cause

newDMWorker() sets autoResume.LatestResumeTime = time.Now() at creation time. On slow CI, the SQLite Init() call can take >1s, meaning by the time the first StageError tick runs, time.Since(LatestResumeTime) ≥ backoff.Current() (initial backoff = DefaultBackoffMin = 1s). This causes CheckResumeSubtask to return ResumeDispatch on the first error tick — before time.Sleep(time.Second) — triggering Resume() on a mock with no registered expectation → panic.

Fix

Reset dmWorker.autoResume.LatestResumeTime = time.Now() immediately before the auto-resume test section. This makes the timing deterministic: the first error tick reliably gets ResumeSkip, and after the time.Sleep(time.Second) the second tick gets ResumeDispatch as intended.

// Reset LatestResumeTime to make auto-resume timing deterministic regardless of test execution speed.
// Without this reset, slow CI environments (e.g., a DB insert taking >1s) may cause the first
// StageError tick to dispatch an unexpected Resume() call before time.Sleep(time.Second) below.
dmWorker.autoResume.LatestResumeTime = time.Now()

// auto resume error
unitHolder.On("Stage").Return(metadata.StageError, ...).Twice()
require.NoError(t, dmWorker.Tick(context.Background()))
time.Sleep(time.Second)
// now Resume() is expected
unitHolder.On("Resume").Return(errors.New("resume error")).Once()
require.EqualError(t, dmWorker.Tick(context.Background()), "resume error")

Close #12545

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

No — test-only change.

Do you need to update user documentation, design documentation or monitoring documentation?

No.

Release note

None

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Flaky: engine/executor/dm TestWorker panics on unexpected mock Resume()</issue_title>
<issue_description>### Go package
github.com/pingcap/tiflow/engine/executor/dm (dir: engine/executor/dm)

Test case

TestWorker (engine/executor/dm/worker_test.go)

Flaky symptom

CI intermittently panics due to an unexpected testify/mock call (Resume()), likely triggered by the auto-resume path in (*dmWorker).checkAndAutoResume.

Failure log / stacktrace

=== Failed

=== FAIL: engine/executor/dm TestWorker (1.35s)

[2026/03/10 10:20:58.178 +08:00] [INFO] [broker.go:104] ["Create new resource broker"] [executor-id=executor-1] [config="{\"local\":{\"base-dir\":\"/tmp/2686613752-localfiles\"},\"s3\":{\"endpoint\":\"\",\"region\":\"\",\"storage-class\":\"\",\"sse\":\"\",\"sse-kms-key-id\":\"\",\"acl\":\"\",\"access-key\":\"\",\"secret-access-key\":\"\",\"session-token\":\"\",\"provider\":\"\",\"force-path-style\":false,\"use-accelerate-endpoint\":false,\"role-arn\":\"\",\"external-id\":\"\",\"object-lock-enabled\":false,\"bucket\":\"\",\"prefix\":\"\"},\"gcs\":{\"endpoint\":\"\",\"storage-class\":\"\",\"predefined-acl\":\"\",\"credentials-file\":\"\",\"bucket\":\"\",\"prefix\":\"\"}}"]

[2026/03/10 10:20:58.178 +08:00] [INFO] [broker.go:133] ["broker will not use s3/gcs as external storage since s3/gcs are both not configured"]

[2026/03/10 10:20:58.187 +08:00] [INFO] [worker.go:149] ["initializing the dm worker"] [job_id=master-id] [worker_id=worker-id] [task-id=task-id]

[2026/03/10 10:20:59.459 +08:00] [WARN] [log.go:102] ["slow log"] [component=gorm] [elapsed=1.272378614s] [sql="INSERT INTO `worker_statuses` (`created_at`,`updated_at`,`project_id`,`job_id`,`id`,`type`,`state`,`epoch`,`error_message`,`extend_bytes`) VALUES (\"2026-03-10 10:20:58.189\",\"2026-03-10 10:20:58.189\",\"\",\"master-id\",\"worker-id\",7,0,2,\"\",\"\") ON CONFLICT (`id`,`job_id`) DO UPDATE SET `updated_at`=`excluded`.`updated_at`,`project_id`=`excluded`.`project_id`,`job_id`=`excluded`.`job_id`,`id`=`excluded`.`id`,`type`=`excluded`.`type`,`state`=`excluded`.`state`,`epoch`=`excluded`.`epoch`,`error_message`=`excluded`.`error_message`,`extend_bytes`=`excluded`.`extend_bytes` RETURNING `seq_id`"] [affected-rows=1]

[2026/03/10 10:20:59.461 +08:00] [INFO] [worker.go:252] ["task stage changed"] [job_id=master-id] [worker_id=worker-id] [task-id=task-id] [from=Initing] [to=Running]

[2026/03/10 10:20:59.461 +08:00] [INFO] [worker.go:257] ["update status"] [job_id=master-id] [worker_id=worker-id] [task-id=task-id] [status="{\"Unit\":\"DMDumpTask\",\"Task\":\"task-id\",\"Stage\":\"Running\",\"CfgModRevision\":0,\"StageUpdatedTime\":\"2026-03-10T10:20:59.461856048+08:00\"}"]

[2026/03/10 10:20:59.463 +08:00] [ERROR] [worker.go:354] ["task runs with error"] [job_id=master-id] [worker_id=worker-id] [task-id=task-id] ["error msg"="[{}]"] [stack="github.com/pingcap/tiflow/engine/executor/dm.(*dmWorker).checkAndAutoResume\n\t/home/jenkins/agent/workspace/pingcap/tiflow/release-8.5/ghpr_verify/tiflow/engine/executor/dm/worker.go:354\ngithub.com/pingcap/tiflow/engine/executor/dm.(*dmWorker).Tick\n\t/home/jenkins/agent/workspace/pingcap/tiflow/release-8.5/ghpr_verify/tiflow/engine/executor/dm/worker.go:174\ngithub.com/pingcap/tiflow/engine/executor/dm.TestWorker\n\t/home/jenkins/agent/workspace/pingcap/tiflow/release-8.5/ghpr_verify/tiflow/engine/executor/dm/worker_test.go:143\ntesting.tRunner\n\t/usr/local/go/src/testing/testing.go:1934"]

[2026/03/10 10:20:59.463 +08:00] [INFO] [worker.go:355] ["got auto resume strategy"] [job_id=master-id] [worker_id=worker-id] [task-id=task-id] [strategy="dispatch auto resume"]

[2026/03/10 10:20:59.464 +08:00] [INFO] [worker.go:359] ["dispatch auto resume task"] [job_id=master-id] [worker_id=worker-id] [task-id=task-id]

panic: 

\tassert: mock: I don't know what to return because the method call was unexpected.

\t\tEither do Mock.On(\"Resume\").Return(...) first, or remove the Resume() call.

\t\tThis method was unexpected:

\t\t\tResume()

\t\t

\tat: [/home/jenkins/agent/workspace/pingcap/tiflow/release-8.5/ghpr_verify/tiflow/engine/executor/dm/unitholder_test.go:309 /home/jenkins/agent/workspace/pingcap/tiflow/release-8.5/ghpr_verify/tiflow/engine/executor/dm/worker.go:360 /home/jenkins/agent/workspace/pingcap/tiflow/release-8.5/ghpr_verify/tiflow/engine/executor/dm/worker.go:174 /home/jenkins/agent/workspace/pingcap/tiflow/release-8.5/ghpr_verify/tiflow/engine/executor/dm/worker_test.go:143] [recovered, repanicked]



goroutine 400 [running]:

testing.tRunner.func1.2({0x9eafd00, 0xc000daa7d0})

\t/usr/local/go/src/testing/testing.go:1872 +0x419

testing.tRunner.func1()

\t/usr/local/go/src/testing/testing.go:1875 +0x683

panic({0x9eafd00?, 0xc000daa7d0?})

\t/usr/local/go/src/runtime/panic.go:783 +0x132

github.com/stretchr/testify/mock.(*Mock).fail(0xc003569028, {0xac45cb2, 0xc1}, {0xc002c37a80, 0x4, 0x...

</details>



<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes pingcap/tiflow#12545

<!-- START COPILOT CODING AGENT TIPS -->
---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our [2 minute survey](https://gh.io/copilot-coding-agent-survey).

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

1. It must be LGTMed and approved by the reviewers firstly.
2. For pull requests to TiDB-x branches, it must have no failed tests.
3. AFTER it has lgtm and approved labels, please wait for the cherry-pick merging approval from triage owners.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[ti-chi-bot]

Hi @Copilot. Thanks for your PR.

I'm waiting for a pingcap member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign d3hunter for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• engine/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[wuhuizuo]

/test ?

[ti-chi-bot]

@wuhuizuo: The following commands are available to trigger required jobs:

/test pull-cdc-integration-kafka-test

/test pull-cdc-integration-mysql-test

/test pull-cdc-integration-pulsar-test

/test pull-cdc-integration-storage-test

/test pull-dm-compatibility-test

/test pull-dm-integration-test

/test pull-syncdiff-integration-test

/test pull-verify

Use /test all to run all jobs.

Details

In response to this:

/test ?

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[wuhuizuo]

/test pull-verify

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-8.5@95dba8c). Learn more about missing BASE report.

Additional details and impacted files

Components	Coverage Δ
cdc	57.5928% <0.0000%> (?)
dm	∅ <0.0000%> (?)
engine	∅ <0.0000%> (?)

Flag	Coverage Δ
cdc	57.5928% <ø> (?)
unit	57.5928% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

@@               Coverage Diff                @@
##             release-8.5     #12546   +/-   ##
================================================
  Coverage               ?   57.5928%           
================================================
  Files                  ?        520           
  Lines                  ?      67406           
  Branches               ?          0           
================================================
  Hits                   ?      38821           
  Misses                 ?      25818           
  Partials               ?       2767           

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[wuhuizuo]

/ok-to-test

[wuhuizuo]

/test ?

[ti-chi-bot]

@wuhuizuo: The following commands are available to trigger required jobs:

/test pull-cdc-integration-kafka-test

/test pull-cdc-integration-mysql-test

/test pull-cdc-integration-pulsar-test

/test pull-cdc-integration-storage-test

/test pull-dm-compatibility-test

/test pull-dm-integration-test

/test pull-syncdiff-integration-test

/test pull-verify

Use /test all to run all jobs.

Details

In response to this:

/test ?

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[wuhuizuo]

/retest

[wuhuizuo]

/test ?

[ti-chi-bot]

@wuhuizuo: The following commands are available to trigger required jobs:

/test pull-cdc-integration-kafka-test

/test pull-cdc-integration-mysql-test

/test pull-cdc-integration-pulsar-test

/test pull-cdc-integration-storage-test

/test pull-dm-compatibility-test

/test pull-dm-integration-test

/test pull-syncdiff-integration-test

/test pull-verify

Use /test all to run all jobs.

Details

In response to this:

/test ?

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[ti-chi-bot]

@Copilot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-syncdiff-integration-test	95579d3	link	true	/test pull-syncdiff-integration-test

Full PR test history. Your PR dashboard.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.