feat: add unit tests for persistent cache task handlers

[BruceAko]

Description

Add unit tests for persistent cache task handlers.

Related Issue

#3892

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.40%. Comparing base (f45351f) to head (bdd4c40).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4023      +/-   ##
==========================================
+ Coverage   34.27%   34.40%   +0.12%     
==========================================
  Files         343      343              
  Lines       40199    40199              
==========================================
+ Hits        13778    13829      +51     
+ Misses      25513    25456      -57     
- Partials      908      914       +6     

Flag	Coverage Δ
unittests	34.40% <ø> (+0.12%)	⬆️

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see 3 files with indirect coverage changes

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[gaius-qi]

LGTM

[chlins]

lgtm