Setting up test suite and adding an example test

[nicholasio]

Description of the Change

This sets up jest tests with 10up-scripts and adds an example test of the example block.

Alternate Designs

Benefits

Unit tests infrastructure and a simple example of a jest test.

Possible Drawbacks

Verification Process

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Changelog Entry