Refine TestInstanceOperation by using verifier.

[xyuanlu]

Issues

• My PR addresses the following Helix issues and references them in the PR description:

#2589

Description

• Here are some details about my PR, including screenshots of any UI changes:

Add verifier for test to add stability.

Tests

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NA

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(If CI test fails due to known issue, please specify the issue and test PR locally. Then copy & paste the result of "mvn test" to here.)

Changes that Break Backward Compatibility (Optional)

• My PR contains changes that break backward compatibility or previous assumptions for certain methods or API. They include:

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Documentation (Optional)

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Commits

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  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Code Quality

• My diff has been formatted using helix-style.xml
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[xyuanlu]

This change is approved by @MarkGaox
Commit message "Refine TestInstanceOperation by using verifier."