Unclear description in official docs creating spy: 'ee.on' ? 'some event' ?

[Dmytro2V]

https://www.chaijs.com/plugins/chai-spies/

What is ee.on ?
and what is 'some event'?

"Creating Spies
In this module, a spy is either an empty function, or a wrapped named function. Once chai has been extended, you can create a spy through chai’s own interface.

function original () {
// do something cool
}

const spy = chai.spy(original);

// then use in place of original
ee.on('some event', spy);

// or use without original
const spyAgain = chai.spy();
ee.on('some other event', spyAgain);"

[keithamus]

The code demonstrates an example of how to use the spy like a function.

In the example ee is assumed to be an instance of Node's EventEmitter. 'some event' is an example event name. The point of the example is to show that spy can be passed around like a regular function.