br: use random port to avoid flaky test (#65186)

[ti-chi-bot]

This is an automated cherry-pick of #65186

What problem does this PR solve?

Issue Number: ref #65185

Problem Summary:

What changed and how does it work?

use random port to avoid flaky test

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

Summary by CodeRabbit

• Tests
  • Improved test reliability by using dynamically assigned network ports.
  • Reduced failures caused by port conflicts during test execution.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Details

Needs approval from an approver in each of these files:

• br/OWNERS

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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 Plus

Run ID: cb4772f3-ff82-4f42-9654-79e5f3bf798c

📥 Commits

Reviewing files that changed from the base of the PR and between 10431d8 and 3ca33f7.

📒 Files selected for processing (2)

• br/pkg/restore/import_mode_switcher_test.go
• br/pkg/restore/internal/import_client/import_client_test.go

---

📝 Walkthrough

Walkthrough

Changes

Restore test port binding

Layer / File(s)	Summary
Ephemeral listener setup and address wiring br/pkg/restore/import_mode_switcher_test.go, br/pkg/restore/internal/import_client/import_client_test.go	Both tests bind TCP servers to ephemeral ports and pass the resolved listener addresses to the fake PD store or import client. Obsolete fmt imports and fixed-port retry loops are removed.

Estimated code review effort: 2 (Simple) | ~10 minutes

Poem

I’m a rabbit with a listener bright,
Choosing free ports in the night.
No fixed numbers to defend,
Each test finds its own endpoint.
Hop, hop—clean setups take flight!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the main change—using a random port to reduce flaky tests—and matches the modified tests.
Description check	✅ Passed	The description mostly follows the template with issue link, change summary, checklist, and release note, though Problem Summary is left blank.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ 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)

Error: can't load config: unsupported version of the configuration: "" See https://golangci-lint.run/docs/product/migration-guide for migration instructions
The command is terminated due to an error: can't load config: unsupported version of the configuration: "" See https://golangci-lint.run/docs/product/migration-guide for migration instructions

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-8.5@10431d8). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #70012   +/-   ##
================================================
  Coverage               ?   55.6645%           
================================================
  Files                  ?       1849           
  Lines                  ?     666288           
  Branches               ?          0           
================================================
  Hits                   ?     370886           
  Misses                 ?     267806           
  Partials               ?      27596           

Flag	Coverage Δ
integration	39.1478% <ø> (?)
unit	65.1937% <ø> (?)

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

Components	Coverage Δ
dumpling	55.3108% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	63.0565% <0.0000%> (?)

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