test: add unit test for manager handler

[BruceAko]

Description

Related Issue

Motivation and Context

Screenshots (if appropriate)

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 52.77%. Comparing base (570a37f) to head (f041879).
Report is 2 commits behind head on main.

❗ Current head f041879 differs from pull request most recent head d765e28. Consider uploading reports for the commit d765e28 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3222      +/-   ##
==========================================
- Coverage   52.82%   52.77%   -0.06%     
==========================================
  Files         192      192              
  Lines       20341    20341              
==========================================
- Hits        10746    10735      -11     
- Misses       8796     8802       +6     
- Partials      799      804       +5     

Flag	Coverage Δ
unittests	52.77% <ø> (-0.06%)	⬇️

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

see 5 files with indirect coverage changes

[BruceAko]

@gaius-qi Updated now. PTAL.

[gaius-qi]

LGTM