Chapter 5. Testing Angular Components

In the chapters so far, we focused on writing our Angular application, and dealt with how to use the Angular CLI, how to create components, some common built-in Angular directives, and the like.

In this chapter, we will take a detour to learn how we can write unit tests for the components we have written so far. To do this, we will first get a sense of the unit testing setup for Angular, the various frameworks and libraries we use to accomplish this, and walk step by step through writing unit tests for a component.

Why Unit Test?

But before we go into all that, let’s quickly talk about unit tests and why they are important. Unit tests are called that because they test an individual unit within your application. Given a very large application and its many pieces, it can become very tricky to test each and every flow through the application. This is why we break up the testing to check each individual component, such that we can be assured that when they are hooked up together, they will work correctly under all cases without necessarily testing each and every flow.

This is easily demonstrated with a simple example. Assume we have a very simple application with three different parts. Each part itself might have five different flows through it, giving us a total of 5 * 5 * 5 = 125 flows through the entire application. If we focused only on end-to-end or overall testing, we would have to test 125 flows (or somewhere approaching that number) to ...

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