feat: add ava unit testing snippets

[savioxavier]

Hello there 👋

I've added a few snippets related to Unit Testing using the Ava test runner framework

Why? Because I believe unit testing is a super-important part of your code and helps you to figure and assert whether your code works as expected. Also, I used Ava because it seems to be what people prefer to use nowadays and is in use across thousands of NodeJS projects. In case you wish to check why Ava is a better alternative, please read this.

Cheers,
Skyascii

[SCHW18TZ]

Hey, thanks for the contribution, it's highly appreciated! Although there is one thing you should keep in mind, all the PRs should be tested and then be made. Did you test this well? Because I think you need to add this file in the package.json file in the root of the repository. Please revert back to me when you have made the changes and we will happily merge this Pull request!