Add functional and unit tests

**Is your feature request related to a problem? Please describe.**
Add functional tests and unit tests to get good code bug coverage

**Describe the solution you'd like**
To use [Testing Library](https://testing-library.com/) and [puppeteer](https://github.com/puppeteer/puppeteer) 

**Describe alternatives you've considered**
None

**Additional context**
N/A
