RxJS unit testing in Angular application. The whole picture.

Name: RxJS unit testing in Angular application. The whole picture.
Rating: 4.3 (139 reviews)

I will make you understand the system - the system of RxJS unit testing tools in Angular applications.

Last updated 10/2019

English

What you'll learn

In-depth look in RxJS unit testing
All possible methods to do unit tests for RxJS code in Angular
Simplest async testing with Jasmine 'done' callback
Testing by using virtual time (RxJS VirtualTimeScheduler) and fake time (Angular fakeAsync helper)
How to avoid additional arguments in methods under test by using AsyncScheduler/delegate trick
What is difference between VirtualTimeScheduler and TestScheduler
What is marble testing and how to use progressive time syntax in marble diagrams
How to reduce code boilerplate by using wrapper libs like jasmine-marbles and rxjs-marbles
What is difference between testing with TestScheduler flush() and new TestScheduler run() method?
Angular demo project with all reviewed code

4 sections • 11 lectures • 54m total length

Introduction2:04
Introduction
RxJS Schedulers5:40
Before we start diving into unit testing - we should clarify what are schedulers in RxJS
You already know that Observables produce values over time. And the moment when exactly value will be emitted is controlled by special entity - scheduler.
Knowing how schedulers work are extremely important in understanding how to unit test you async code
Possibly you already know that topic - but plz don’t skip - recalling that will help us to be on the same page.

Testing with Jasmine 'done' callback5:52
Jasmine framework provides a special ‘done' callback to testing async code.
How to apply it to Observables? Let's find out.
Testing by using RxJS VirtualTimeScheduler7:32
In a previous lesson, we reviewed jasmine and its done callback for testing.
But noticed that it is not good for big delay values.
And this is where VirtualTimeScheduler can help us.
It provides a virtual time mechanism so you can emulated passed time inside RxJS scheduler to run delayed tasks instantly.
Testing by using Angular fakeAsync function4:40
Besides the methods we reviewed previously - angular also has another possible way of testing observables that use asyncScheduler.
For that method, fakeAsync helper function is used.
VirtualTimeScheduler vs TestScheduler in RxJS3:01
Before we start getting deeper in TestScheduler usages We have to understand how it differs from VirtualTimeScheduler.
I’ve already told you that TestScheduler inherits from VirtualTimeScheduler.
So you may think that we can use TestScheduler in the same way as VirtualTimeScheduler.
And you are right!

Marble testing with TestScheduler7:43
Another testing method that is more visual and allows us to write tests in a more obvious way is marble testing. In that method, all observable sequences are represented as marble diagrams.
And RxJS TestScheduler has special methods that give us the possibility to create tests with marble diagrams.
Marble testing with jasmine-marbles3:28
Jasmine-marbles is just a wrapper library for RxJS TestScheduler.
So it provides the same functionality.
But also it brings some amenities to make tests code shorter.
Marble testing with TestScheduler.run6:04
Starting from RxJS ver6 TestScheduler has a special method 'run' which allows time progressive syntax in marble digrams.
So we can specify explicitly delay values in a convenient manner.
Let's take a closer look.
Marble testing with rxjs-marbles lib5:23
In one of the previous lessons, we reviewed jasmine-marbles.
But there is one more wrapper library: rxjs-marbles.
Does it provide the same functionality or can it do even more?
Let's find out that.

If you already tried to code unit tests for Observables - then you may be overwhelmed with a variety of methods on how to do that.

Which one is right for you?

Will it be jasmine with 'done' callback which we usually use for async code?

Or maybe TestScheduler?

Or you are going to use jasmine-marbles which is being mentioned in official Angular documentation?

I am not even naming other methods.

What is common for them and where they differ? How to put all of them in one solid picture in your head?

This is what I am going to do in my lessons - I will make you understand the system.