Make verifier return type as ActionResponse

[heemin32]

Description

According to the comment, verifier should return either a subclass of ActionResponse or null. With previous signature, it can only return null. This commit allows the verifier to return a subclass of ActionResponse so that test case can return a desired ActionResponse.

Issues Resolved

N/A

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[heemin32]

A change in test code. CHANGELOG update is not required.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/14052/
• CommitID: 9d5e67d
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: TIMEOUT ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/14147/
• CommitID: 9d5e67d
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[dblock]

@heemin32 please look at gradle check changes?

[heemin32]

Test failed with com.amazonaws.SdkClientException: Unable to execute HTTP request: Read timed out. Seems like transient issue. Let me rebase the code and see if it pass.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/14233/
• CommitID: 0da7b32

[codecov-commenter]

Codecov Report

Merging #7167 (0da7b32) into main (c1026e3) will decrease coverage by 0.03%.
The diff coverage is n/a.

📣 This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

@@             Coverage Diff              @@
##               main    #7167      +/-   ##
============================================
- Coverage     70.63%   70.60%   -0.03%     
- Complexity    59480    59482       +2     
============================================
  Files          4859     4859              
  Lines        285492   285492              
  Branches      41143    41143              
============================================
- Hits         201645   201564      -81     
- Misses        67270    67344      +74     
- Partials      16577    16584       +7     

Impacted Files	Coverage Δ
...a/org/opensearch/test/rest/RestActionTestCase.java	79.31% <ø> (ø)

... and 469 files with indirect coverage changes

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[heemin32]

@dblock Could you review?

[dblock]

Are you going to use this in a future PR or another repo? Seems innocent enough so we can merge, but maybe next time also bring the new usage in in the same place.

[heemin32]

One example where return value is needed. https://github.com/opensearch-project/geospatial/pull/271/files#diff-f8b944446745642b4f5a7cb15be03faa0045246ee03fb3b99f006b941d04049aR214

Without return value, cannot test the code in listener unless we extract that part as a separate method and make it as visible for testing.

[dblock]

Thanks @heemin32. If you think it's useful, consider adding something in this repo so that we don't break it in the future.