Rather than reworking the whole process from start to finish, Microsoft has a really good guide for the initial setup located here:
One further step .. I decided to use JetBrains WebStorm as my IDE, so that's what these screenshots are from.
This will get you to a functioning example where you can push a button and turn cells green. Hooray! Sort of like Hello World, you have a basic add-in that interacts with Excel through a web page.. But, I really wasn't quite ready to start building things ..
Notably in the instructions, it tells you NOT to use unit tests. Well, I wanted unit tests so, I turned to the jest library.
Step one for this process is to actually install the Jest package with npm with
npm install --save-dev jest
The next step is some manual updating of the highest level package.json file.
The "dependencies" property needs a "jest": "^23.6.0" entry while the "scripts" property needs "test": "jest". At this point, my package.json looked like this:
The next step is to add a new folder called "tests" to the parent directory. This is the folder that jest will look for your tests in. Within that folder I've created a dummy test file with one simple test that simply checks to see if 1 equals 1, so I can know that my test command works.
At this point, I've set up my initial unit testing framework successfully and can confirm my results by going to my terminal and executing "npm run test".
The next challenge that I undertook was incorporating Vuetify and vue-router into my add-in so that my developer could build me some pretty features. Whew .. we'll come back to that one in a few days.