Visual Studio Code virtualization

I'm not sure how to made this clear so I'll start with analogy...

Lets consider I'm writing a web app. In order to test it manually I need to start a server, open the app in browser and take a look at it to visually match a picture with some "reference".

If I want to automate this process I need to write a test that start a server, launch some "virtual browser" like puppeteer, open the app in it and compare the screenshots.

But now lets consider I'm working on some JavaScript package and I want to make sure that intellisense in VSCode works as expected. Despite the code might works well the intellisense still may be broken due to some tricky cases like this:

const require2 = require;
const fs = require2("fs");

In order to manually test support of this "user experience" I need to open the VSCode. Then I need to put some code like fs. and take a look at it to check that there is a popup with autocomplete stuff.

So, what about automation of this process? Is there anything like "virtual VSCode"? Like a tool where I can create an instance of editor, put some code and check if it display the popup.

What is the best approach to test this kind of stuff today?