[Backport 2.x] added UT for validation API related components

[opensearch-trigger-bot]

Backport f95f52b from #252

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (2.x@769a0d6). Click here to learn what that means.
The diff coverage is n/a.

❗ Current head f95f52b differs from pull request most recent head 64146b2. Consider uploading reports for the commit 64146b2 to get more accurate results

@@          Coverage Diff           @@
##             2.x     #271   +/-   ##
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  Coverage       ?   51.32%           
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  Files          ?      150           
  Lines          ?     4959           
  Branches       ?      969           
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  Hits           ?     2545           
  Misses         ?     2161           
  Partials       ?      253           

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