Angular Unit Testing
By executing a piece of automated code that calls a unit of work, unit testing ensures that your application functions as intended (a separate piece of code). Based on a presumption about how that unit of labor would behave, the test will either pass or fail (we call this the code under test).
It is not surprising that unit testing in Angular has some significant differences even if unit testing across frontend frameworks adheres to the same fundamental principles. The ability to unit test takes practice and perseverance to master. Here are 5 simple suggestions to help you learn how to build unit tests in Angular faster: Write your tests before the implementation code, test logic rather than the DOM, test in isolation, write granular tests, and be aware of Angular dependencies.
Recognize Angular Modules and Dependencies
The first piece of advice is to spend some time learning how Angular manages dependencies. To successfully test in isolation, you must first identify dependencies, which are covered in this advice.
The Module architecture of Angular is a little unusual and is perhaps one of the most difficult concepts for beginners to grasp. ES Modules, a method for sharing code between files, are the foundation upon which Angular Modules are constructed. At its heart, a module is just a means of importing and exporting code for use by other files. Although ES Modules and Angular Modules operate differently, the fundamental concept is the same in both cases.
Dependencies that other programs (components, services, etc.) can use are listed in Angular Modules. For instance, a reusable button component must be registered in the appropriate Angular Module in order to be used and consumed in your application. The compiler will throw an error if it isn’t. Why is this crucial? And now, on to the second piece of advice.
Test in Isolation
When a unit is being tested in isolation, it should be kept apart from other application components. What does this mean when we discuss Angular unit testing? All other dependencies on the object you are testing (be it a component, service, pipe, etc.) should be segregated or mocked. It makes logic if you think about it.
We simply want to test a portion of the program; we don’t want to test the complete thing. The purpose of unit testing is exactly that!
If you don’t run your tests in isolation, you’ll have to spend hours sorting through cryptic console warnings to determine why (and where!) your tests are failing.
As was previously said, you must mock out dependencies in order to test independently. Because of this, it’s crucial to comprehend how Angular manages dependencies. Dependence could be a service that is injected, a component that you use, or a variety of other things.
Write Granular Unit Tests
Third, I advise you to create a few quick, independent unit test cases. It can be tempting to create an all-encompassing test scenario where you call an implementation function and set up several assumptions in a single unit test. When several assertion tests fail, it might be challenging to figure out what went wrong.
Determine how a single unit might be divided into many test cases rather than defaulting to the all-encompassing single test case scenario (if the situation calls for it). You can easily write two or three test cases rather than a single, bloated test, for instances where a component function subscribes to service and modifies the local component state with the result.
Test Logic, Not DOM
This advice might be a little debatable. Unit tests can assert that specific behavior was carried out by performing an operation (like as clicking) and searching the DOM for elements. Although I believe that this kind of structure is appropriate in some circumstances, it shouldn’t be the rule. You might wish to assign those jobs to an End-to-End (E2E) test if you frequently write a lot of DOM queries in your tests.
Think of the traditional calculator as an example, which has numerous buttons for different mathematical calculations. When a button is pressed, data is changed, and a new sum or number is shown on the screen. This situation is ideal for a unit test! Each time a button is pressed, data changes; the calculator uses input to make an output.
On the other hand, it happens frequently that a button will direct the user to another website or cause something else to appear or disappear. These scenarios depict application functionality rather than just changing data, making them excellent opportunities to create E2E tests.
Test First, Code Second
The last, and possibly most crucial, step is to discipline yourself to write your unit test cases before you develop the logic for the component or service. Does that seem strange? It’s acceptable if it does since, in a way, it’s backward.
Test-Driven Development is the practice of writing tests first (TDD). TDD allows the test scenario to drive the implementation of the code rather than the implementation code dictating how the unit test is written. Because of this, TDD-style code is typically cleaner and less bloated.
