[ZEPPELIN-6485] Add unit tests for PropertiesUtil

[uommou]

What is this PR for?

This PR adds unit tests for PropertiesUtil in the zeppelin-interpreter module.

The tests cover the behavior of getString, getLong, and getInt, including missing properties, empty and whitespace-only values, successful numeric parsing, parsing failures, and numeric boundary values.

No production code is changed.

What type of PR is it?

Improvement

Todos

• Add tests for missing properties
• Add tests for empty and whitespace-only values
• Add tests for valid positive and negative numeric values
• Add tests for numeric boundary values
• Add tests for invalid and out-of-range numeric values

What is the Jira issue?

https://issues.apache.org/jira/browse/ZEPPELIN-6485

How should this be tested?

Run the new unit tests:

./mvnw test -pl zeppelin-interpreter -Dtest=PropertiesUtilTest

Expected result:

Tests run: 6, Failures: 0, Errors: 0, Skipped: 0
BUILD SUCCESS

Screenshots (if appropriate)

This PR does not change the user interface.

Questions:

• Does the license files need to update? No.
• Is there breaking changes for older versions? No.
• Does this needs documentation? No.

[voidmatcha]

LGTM 👍