Write more tests for backend to improve the test coverage

[ZihengSun]

Expand more tests in this folder to cover more logic in the Java backend code

https://github.com/ESIPFed/Geoweaver/tree/master/src/test/java/com/gw

Currently, our coverage is not that good. Need to find those least covered code and increase their test coverage.

The test coverage report is generated in every Github action workflow run: https://github.com/ESIPFed/Geoweaver/actions/runs/8793951982/job/24132616837#step:6:12