FE & BE: Add test coverage

[tholulomo]

Currently, on the frontend app, .js files are exempted from testing, especially on FE. Add test for all .js files in both BE & FE. Also, BE & FE does not have a code coverage report for developers to see and understand the coverage status. This is available in our CI pipeline

Acceptance Criteria:

1. Refactor where necessary
2. Add coverage report after each test for both FE & BE
3. Our next target is to have 80% and above code coverage