add jest config and sample test file

[njogz]

Description

Add jest configuration and one unit test

medic/interoperability#33

Code review checklist

• [ ] Readable: Concise, well named, follows the style guide, documented if necessary.
• [ ] Documented: Configuration and user documentation on cht-docs
• [ ] Tested: Unit and/or e2e where appropriate
• [ ] Backwards compatible: Works with existing data and configuration or includes a migration. Any breaking changes documented in the release notes.

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.

[njogz]

Thanks for the comments @lorerod. I have replied to both of them. As for Mocha vs Jest: Jest is designed for simplicity and we can get most if not all relevant tests done with Jest as well as getting a code coverage report without adding other libraries.

[njogz]

@andrablaj I have addressed your comments please have another look.

[njogz]

@lorerod I am working on some documentation for the choice of testing framework and the location of the test files. Do you need that before you can approve this PR?