planner: encapsulate task dir and move test related code to test file

[AilinKid]

What problem does this PR solve?

Issue Number: ref #51664

Problem Summary:

What changed and how does it work?

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

[tiprow]

Hi @AilinKid. Thanks for your PR.

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[codecov]

Codecov Report

Merging #52083 (bb55d72) into master (02b277a) will decrease coverage by 15.9852%.
Report is 5 commits behind head on master.
The diff coverage is 100.0000%.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #52083         +/-   ##
=================================================
- Coverage   70.6793%   54.6941%   -15.9852%     
=================================================
  Files          1486       1599        +113     
  Lines        439458     609511     +170053     
=================================================
+ Hits         310606     333367      +22761     
- Misses       109346     252904     +143558     
- Partials      19506      23240       +3734     

Flag	Coverage Δ
integration	36.7629% <ø> (?)
unit	70.4351% <100.0000%> (-0.0499%)	⬇️

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

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	51.4294% <ø> (+5.6106%)	⬆️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, qw4990

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-26 07:48:36.754696203 +0000 UTC m=+1967743.776942591: ☑️ agreed by hawkingrei.
• 2024-03-26 07:51:09.934350076 +0000 UTC m=+1967896.956596456: ☑️ agreed by qw4990.