javascript. Assembly with tests. How to do minimal testing of simple code?

Question

JavaScript

Tell me a link or maybe a small assembly on the repository where some simple JS code (ideally on vue.js but not necessarily) was overlaid with some kind of simple test, webpack for example with mocha or any other option. Test for drop-down of an element in a larger number of lines (10 thousand).
It is enough to test some function of one. For speed or something. I have not done tests yet, I need an example for quick reference.
To run tests with their package.json command, as I understand it.
And maybe someone knows a third-party free API json file, so that there would be at least 10 thousand lines of a list, simple objects or anything.
All this should be displayed in a drop-down element, such a strange wish of the customer.