Write unit tests

[Esemesek]

There is quite a bit of logic in lib directory, but there are no unit tests to verify if nothing is broken. Lack of unit tests makes it harder to refactor/change existing code.

TODO

• - Implement unit tests for lib/helpers - This is the most important one because most of logic exists here
• - Implement unit tests for lib/LinearGradient
• - Implement unit tests for lib/RadialGradient

[yeswanth]

I would like to start on lib/helpers with tests to check simple functions (to begin with). Will be using jest for testing. I am maintaining a document with the test plan in this spreadsheet.