Unittest for pinnedpost.dart

[nidhin29]

This change included the Unittest for pinned post

Issue Number: #2161

Fixed #2161

Did you add tests for your changes?

Yes

Summary

It is unittest for pinned_post.

Does this PR introduce a breaking change?

No, this does not introduce any major changes to the codebase.

Have you read the contributing guide?

Yes, i have followed the guidelines.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6dd96ef) 80.28% compared to head (62bcf5a) 80.41%.
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2241      +/-   ##
===========================================
+ Coverage    80.28%   80.41%   +0.12%     
===========================================
  Files          149      149              
  Lines         6986     7006      +20     
===========================================
+ Hits          5609     5634      +25     
+ Misses        1377     1372       -5     

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