Add testing framework to write test cases

[tomarsachin2271]

After searching different testing framework, Jest seems to be the best choice so far as it supports mocking, asynchronous testing, parallel test execution in an easy way.

[kanthgithub]

it would be easier if we start adding unit tests for Decoders as and when we write it
i will try to start adding tests to decoders i have pickedup

** after the merge of AA25 PR, i will make sure all commits to have some basic tests