Automated tests for the theme

[paulpopus]

We can write some tests using Mocha.js that will test that the theme runs as expected. First issue is to make sure it compiles but other suggestions are welcome.

EDIT:

Going to open a PR early so others can try the mocha tests.

Copying in @finnlewis @Adnan-cds @stephen-cox @cjstevens78

Branch
feature/automated-theme-tests

Usage
npm install the new packages then try running npm run health-check and hopefully all tests pass. These tests check specifically for the theme structure, checking if directories and files exist and that gulp commands return with no errors.

Left to do:

• Test for Browsersync and gulp watchers
• Test for generated files and making sure that they compile as expected
• File cleanup after tests
• Integrate with Github Workflows
• Post installation tests, these are tests that check things like node env and any other things the dev might need to check after running npm install such as node_modules being gitignored.

Can continue working on this later but was keen to get first impressions and comments. There is a related PR in draft mode for this.