Added unit testing using jest

[sauk2]

Closes #7

Summary

Added jest for unit testing. Unit tests can be found in __test__ folder.

Unit testing locally

Run the following command to run the unit tests and code coverage locally.

 npm run test

[sauk2]

We need to execute the npm test as part of our CI loop in the GitHub actions. I recommend to give a look into the test.yml in setup.ros and the use of build-and-test.sh script.

Added a job in test.yml that builds the package and runs unit tests.