- Hello again and welcome to lesson four.
This lesson is all about testing asynchronous code.
This is a really important aspect
in industrial-strength web applications.
We'll begin by testing asynchronous code
that invokes a callback when it's finished.
We'll see how to verify the callback is invoked correctly.
We'll also see how to specify an extended time mode,
which is important if your code is particularly slow.
Next up, we'll see how to test promises.
We'll recap how promises work.
We'll see how to test promises,
and we'll see how to use the async and the await keywords
to simplify how we handle promises
in our code and in our tests.
To finish off the lesson, we'll take a look
at Rxjs, reactive extensions for JavaScript.
This library introduces the concept of observable objects.
We'll explain how to use these
and how to test them in our Jest application tests.