Boost Unit Test Coverage to over 90%.

My codebase runs on a React frontend and an Express backend, and every test is written in Jest. Right now overall coverage hovers around 15 %, so I need a seasoned test-writer to push that figure well past 90 %.

Some suites already exist, but many are failing or incomplete; others are missing entirely. Your job is to repair what’s broken and then add the missing unit tests so every critical component and helper function is exercised.

Key points you should know while planning your work:
• React components rely heavily on hooks and context, so you’ll need solid experience with @testing-library/react and mocking utilities.
• The Express layer uses middleware chains, custom error handlers, and a few external services that will need to be stubbed or mocked.
• All assertions, mocks, and spies must remain in plain Jest—no additional test runners.

Acceptance will be based on:
1. An npm script that produces an easily readable coverage report showing > 90 % lines and branches for both frontend and backend.
2. All existing tests passing without skipped or todo blocks.
3. New tests committed with clear, descriptive names and no overlap or dead code.
4. No changes in application behaviour outside the test environment.

If this sounds straightforward to you, let’s get the suite green and the coverage high.