refactor: improve validation for search route and refactor test code

[JadenKim-dev]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

When invalid request body is sent to the search route, the error message returned is ambiguous.
It makes it difficult to determine from the message which part of the request is invalid.

Test cases for validation are not grouped in detail, making them difficult to understand.

Issue Number: N/A

What is the new behavior?

More detailed error message is returned, allowing clients to identify where the validation failed for search route.
Each test case is grouped so that one can understand what tests are being performed just by looking at the test results.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Additionally, I removed duplicated logging and validation logic.
For now test coverage for line improved to 100%.