Implement Test Coverage for Existing Functions Across the Codebase

Description
The project currently has little to no automated test coverage.

Review the testing approaches used in the CELTS and LSF projects and begin building a test suite for this project using similar patterns where appropriate. The goal is to establish reliable coverage for current behavior.

Scope
Review existing test structure and conventions used in CELTS and LSF.
Set up the project's test framework and directory structure if needed.
Add tests for existing functions throughout the application.
Prioritize core business logic and frequently used functionality first.
Include both successful and failure/edge-case scenarios where applicable.
Add integration tests for functions that interact with the database or multiple application components.
Ensure tests can be run consistently in the local development environment which means to ensure test data exist too.

Review the testing approaches used in the CELTS and LSF projects, then inspect this project's existing structure and conventions. Identify the needed test framework and directory layout before adding coverage for prioritized core and frequently used functions, including success, edge-case, database, and integration scenarios. Done means tests run consistently in the local development environment with required test data.

Written by the indexing model from the issue text.