Create Exceptionhandler & ExceptionHandlerTest classes

[Krushit-Babariya]

Exception Handling

1. Exception Handling (ExceptionHandler class):
The ExceptionHandler class is annotated with @ControllerAdvice, which allows it to handle exceptions globally for the entire application. It has handlers for the following exceptions:
NoSuchElementException: Returns a 404 Not Found response when an element, such as an employee, is not found.
IllegalArgumentException: Returns a 400 Bad Request when an invalid UUID or other bad input is encountered.
MethodArgumentNotValidException: Handles validation errors, capturing invalid input fields and their associated messages, returning a 400 Bad Request.
Generic Exception: Catches all other unhandled exceptions, returning a 500 Internal Server Error.

2. Unit Testing (ExceptionHandlerTest class):
The ExceptionHandlerTest class contains unit tests to ensure that each exception handler in the ExceptionHandler class behaves as expected. It tests:
Correct handling of NoSuchElementException, ensuring it returns a 404 status.
Handling of IllegalArgumentException, verifying a 400 status.
Proper validation error handling (MethodArgumentNotValidException) by mocking field validation and checking that it returns the appropriate errors.
A generic Exception handler that ensures unexpected errors result in a 500 Internal Server Error.

[Krushit-Babariya]

Review Changes..!

[mfvanek]

See

java-experiments/spring-boot-app-example/src/test/java/io/github/mfvanek/pg/cluster/controllers/EmployeeControllerTest.java

Line 29 in be54c83

.expectStatus().isNotFound()

I've already have a test that works without this ExceptionHandler.
Prove to me the necessity and usefulness of your code through an integration test.