Add code coverage with nyc tool with HTML support

[anuragparida]

Used nyc tool by IstanbulJS to provide Code coverage with added functionality of HTML support (see below)-

• Employed method to generate HTML file in ./coverage depicting Code Coverage results in both CLI format and Graphical format.

• Run the coverage command with sudo npm test to view the coverage details in the CLI and generate an HTML file in ./coverage.

• View the Graphical data by opening ./coverage/index.html in a web browser.

• You can then browse the directory structure to see which files failed the tests.