The asynchronous testing

In this section, you'll learn how to test asynchronous functions. The process of testing asynchronous functions isn't that different from synchronous ones, like what we've done already, but it is a little different so it justifies its own section.

Creating the asyncAdd function using the setTimeout object

To kick things off, we'll make a fake async function using setTimeout to simulate a delay inside utils.js. Just below where we make our add function, let's make one called asyncAdd. It'll essentially have the same features, but it'll use setTimeout and it'll have a callback to simulate a delay. Now in the real world, this delay might be a database request or an HTTP request. We'll be dealing with that in the following chapters. For now though, let's add module.exports.asyncAdd:

module.exports.add = (a, b) => a + b;

module.exports.asyncAdd = ()

This will take three arguments, as opposed to the two the add function took, a, b, and callback:

module.exports.add = (a...