Unit Testing functions in `meta-analysis` sub-workflow

[meetagrawal09]

Description

This PR aims at adding unit tests for all the pivotal function in the meta-analysis sub-workflow.

Review Time Estimate

• [ ] Immediately
• [ ] Within one week
• [X] When possible

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] My name is in the list of CITATION.cff
• [ ] I have updated the CHANGELOG.md.
• [ ] I have updated the documentation accordingly.
• [X] I have read the CONTRIBUTING document.
• [] I have added tests to cover my changes.
• [X] All new and existing tests passed.