Add Unit Tests with Jest and Integrate with CI Workflow

[teles]

The project lacks unit tests. Adding unit tests with Jest and integrating them into the CI workflow will improve code quality and reliability. Additionally, adding a coverage badge will help monitor test coverage.

Requirements:

• Configure Jest as the testing framework.
• Add tests for core functionalities.
• Provide instructions to run tests (e.g., npm test).
• Integrate tests into the CI workflow.
• Add a coverage badge to the README.

Acceptance Criteria:

• Jest configured.
• Core functionalities covered by tests.
• Test instructions in README.
• Tests run successfully.
• CI workflow updated to run tests.
• Coverage badge added to the README.

Resources:

• Jest Documentation