Improve the job-scheduler code coverage percentage

[prudhvigodithi]

Is your feature request related to a problem?
From https://app.codecov.io/gh/opensearch-project/job-scheduler the existing Coverage is 29.17%.

What solution would you like?
Improve the repo code coverage percentage incrementally to ensure the code has enough test coverage.

What alternatives have you considered?
A clear and concise description of any alternative solutions or features you've considered.

Do you have any additional context?
Add any other context or screenshots about the feature request here.

[zelinh]

[Grooming] We can add incrementally to improve the code coverage.