Unit testing is important to verify the behavior of the smallest units of code in your application. It helps improve the quality of your code and reduces the amount of time and money you spend on bug fixing. Moreover, unit testing helps you find bugs early on in the development life cycle and increases your confidence in the code. This post we’ll show you how to get started with Node.js unit testing in practice, with examples. Think of this post as a “hello world” for unit testing in Node.js.
We’ll start with the “what” of Node.js unit testing, explaining the concept of this form of testing. After that, we move to the “why”, so you can understand what’s the value you gain by adopting unit testing. Then, the next natural step is the how of unit testing in Node.js: you’ll see how to get started with unit testing in the quickest possible way. For the tutorial part of the post, we’ll assume two things:
- You have Node.js installed on your machine
- You’re comfortable using the command line.
After that, we’ll cover several topics:
- more benefits of Node.js unit testing
- the anatomy of a Node.js unit testing
- a comparison between some of the most popular Node.js testing frameworks
- useful tips for writing great Node.js tests
Finally, we give you a summary of what you’ve learned. Before wrapping up, we share some final tips on what to do next.
First of all, let’s discuss what is Node.js unit testing in the first place.
What Is Node.js Unit Testing?
Let’s start with some definitions. Node.js unit testing is simply unit testing made to Node.js applications. That’s the obvious definition, but kind of useless if you’re not familiar with the concept of unit testing itself, so let’s go further.
Unit testing is one of the most important types of automated testing. It focuses on examining the smallest parts of code—the so-called units—by isolating that code. Since unit tests exercise isolated units, that means the system under test can’t interact with external dependencies, such as databases, the file system, or HTTP services. During tests, such dependencies are replaced by “fake” implementations, such as mocks/stubs/spies, which are collectively known as test doubles.
Due to the restrictions above, unit tests are typically easy to write and can be executed with almost no configuration, as they are often made of just one function call. Besides that, it’s easy to collect and display results from unit tests. It’s important to write unit tests in a way that tries all possible outcomes of a snippet of code. In each unit test, the returned value of the unit must equal the expected value. If that’s not the case, then your test will fail.
Next, let’s learn about the reasons behind doing Node.js unit testing.
Why Do You Need Testing?
Node.js unit testing helps you to guarantee the quality of your product. Imagine you launch a new application that requires the user to sign up. First of all, the user has to fill in all their data. Next, they hit the signup button to submit their profile. However, the application returns an error message, and the user isn’t able to sign up.
This example shows the importance of testing your business logic. The easiest way to test your business logic is by using unit testing because it tests the smallest units of code in your application.
Besides that, unit tests are great for catching regressions. “Regression” is the name we give to the phenomenon of new changes to the codebase causing problems in other parts of the application. Without unit testing—and automated testing in general—you would need to comprehensively test your complete app by hand after every change. This would be highly impractical to so. Fortunately, unit testing can be leveraged in this scenario. A comprehensive suite of unit tests—which run in your CI/CD pipeline—acts as a great safety net for developers.