Add PetValidator unit and integration tests

[wickdynex]

Title:

Add PetValidator unit and integration tests

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Description:

This PR add PetValidatorTests to test whether the class PetValidator works as expected. Tests including unit and integration tests.

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Problem:

The project is lack of a unit test for PetValidator class. Without proper testing, the validator’s functionality may go unverified

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Solution:

• Add new test: add test file to check each methods of PetValidate.

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Type of Change

• New feature

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Changes:

• Add test class named PetValidatorTests to check PetValidator work.

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Local Test ScreenShot:

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Additional Information:

If there are any bad design patterns, design approaches, or bugs in this PR😵‍💫, please point them out, and I will make the necessary changes🥰.

Followed Question:

1. Need I update the Copyright year at the top of each I've modified files?
2. Need I refactor the Validate process, use Spring Bean Validation instead of PetValidation class?
   plz give some idea🤩.