Add tests to RegisterPagingSource

[sharon2719]

IMPORTANT: Where possible all PRs must be linked to a Github issue

Fixes [link to issue]

Engineer Checklist

• [ ] I have written Unit tests for any new feature(s) and edge cases for bug fixes
• [ ] I have added any strings visible on UI components to the strings.xml file
• [ ] I have updated the CHANGELOG.md file for any notable changes to the codebase
• [ ] I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the project's style guide
• [ ] I have built and run the FHIRCore app to verify my change fixes the issue and/or does not break the app
• [ ] I have checked that this PR does NOT introduce breaking changes that require an update to Content and/or Configs? If it does add a sample here or a link to exactly what changes need to be made to the content.

Code Reviewer Checklist

• [ ] I have verified Unit tests have been written for any new feature(s) and edge cases
• [ ] I have verified any strings visible on UI components are in the strings.xml file
• [ ] I have verifed the CHANGELOG.md file has any notable changes to the codebase
• [ ] I have verified the solution has been implemented in a configurable and generic way for reuseable components
• [ ] I have built and run the FHIRCore app to verify the change fixes the issue and/or does not break the app

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 28.2%. Comparing base (1a3dbd4) to head (d2c814c). Report is 2 commits behind head on main.

Additional details and impacted files

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