test: stabilize flaky TestTxnGoString

[flaky-claw]

What problem does this PR solve?

Issue Number: close #69877

Problem Summary:
Flaky test TestTxnGoString in tests/realtikvtest/txntest intermittently fails, so this PR stabilizes that path.

What changed and how does it work?

Root Cause

TestTxnGoString had a storage-independent GoString assertion coupled to RealTiKV setup, so external PD/TiKV availability could fail the case before the intended behavior was exercised.

Fix

testkit.CreateMockStore(t) preserves the same begin/insert/rollback LazyTxn state transitions while removing unrelated external setup dependency.

Verification

Spec:

• target: tests/realtikvtest/txntest :: TestTxnGoString
• strategy: tidb.go_flaky.default
• plan mode: BASELINE_ONLY
• requirements: required case must execute; no skip; repeat count = 1
• execution surface: GO_TEST_WITH_TAGS
• build tags: intest, deadlock
• baseline gates: required_flaky_gate, build_safety_gate, intent_guard_gate
• feedback surface source: baseline_only

Observed result:

• status: passed
• required case executed: yes
• submission decision: ALLOWED
• note: Required flaky case executed during validation.
  Required flaky case was not skipped.
  target_flaky_exact passed.
  build passed.

Gate checklist:

• target_flaky_exact: PASS
• unavailable_pd_diagnostic: SKIPPED
• package_contract_advisory: SKIPPED
• build: PASS

Commands:

• go test -json -tags=intest,deadlock ./tests/realtikvtest/txntest -run '^TestTxnGoString$' -count=1
• make build

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

Fixes #69877

Summary by CodeRabbit

• Tests
  • Updated transaction formatting test setup while preserving existing assertions.

[ti-chi-bot]

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: d8ef7283-e0b1-4b9c-b95d-7aebbdbce173

📥 Commits

Reviewing files that changed from the base of the PR and between 531e40c and 46fe755.

📒 Files selected for processing (1)

• tests/realtikvtest/txntest/txn_test.go

---

📝 Walkthrough

Walkthrough

TestTxnGoString now creates its mock store with testkit.CreateMockStore(t) instead of the real-cluster setup helper; its assertions remain unchanged.

Changes

Transaction string test

Layer / File(s)	Summary
Mock store initialization tests/realtikvtest/txntest/txn_test.go	TestTxnGoString uses testkit.CreateMockStore(t) while retaining the existing transaction string assertions.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• pingcap/tidb#68794: Changes test mock-store construction using related testkit helpers.

Suggested labels: approved, lgtm

Suggested reviewers: lcwangchao

Poem

I swapped one store helper with care,
While string checks stayed nestled there.
No assertions flew, no formats changed,
The test’s small setup was rearranged.
— A tidy rabbit hops away 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the change to stabilize TestTxnGoString.
Description check	✅ Passed	The description includes the issue, problem summary, change details, tests, and release note.
Linked Issues check	✅ Passed	The PR addresses the flaky TestTxnGoString test described in issue #69877.
Out of Scope Changes check	✅ Passed	The code change is limited to the test setup needed to stabilize the targeted flaky test.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="Running error: context loading failed: failed to load packages: failed to load packages: failed to load with go/packages: context deadline exceeded"
level=error msg="Timeout exceeded: try increasing it by passing --timeout option"

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[ti-chi-bot]

@flaky-claw: 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
idc-jenkins-ci-tidb/check_dev_2	46fe755	link	true	/test check-dev2

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.0036%. Comparing base (531e40c) to head (46fe755).

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #69878        +/-   ##
================================================
- Coverage   76.3207%   74.0036%   -2.3171%     
================================================
  Files          2041       2056        +15     
  Lines        559975     578270     +18295     
================================================
+ Hits         427377     427941       +564     
- Misses       131697     150003     +18306     
+ Partials        901        326       -575     

Flag	Coverage Δ
integration	40.7442% <ø> (+1.0389%)	⬆️

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

Components	Coverage Δ
dumpling	60.4471% <ø> (ø)
parser	∅ <ø> (∅)
br	47.4060% <ø> (-15.3154%)	⬇️

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