Testing is a major part of JavaScript programming.

Testing helps developers avoid introducing bugs and defects in their projects, which

if deployed to production could cost them or their company money in returning users.

As developers add new features to a website or

app, they test that a feature works and that nothing else broke in the process.

They might use a combination of testing methods for this.

For example, they'll code a small part of their program, refresh the app or site and

interact with it to test if everything works as expected.

And they'll check for runtime errors and warning messages in the console.

This manual testing process works but it can be slow and error prone.

And it doesn't always prove that your logic works.

There might be times when you're unsure of what went wrong or how to fix it.

So how can developers prove that each piece of their code does what they want?

In many cases, developers programmatically test the code and

features in their project to ensure expected behavior.

They write special functions called unit tests to check if each part of their

program works, even in edge cases or extreme operating parameters.

They first identify the expected outcomes of every part of their program,

individual functions for example, and

write tests against them to make sure those parts work as intended.

For instance, they'll write a test that checks if a function exists, and

a test that checks a function's behavior when given a certain set of inputs.

The tests make sure that each function gets called with the required arguments

and returns the correct result.

Writing JavaScript unit tests from scratch, especially on big projects,

tend to be limited, hard to implement, and time consuming.

So the wonderful JavaScript community once again has our backs.

They've created libraries and frameworks that let you quickly write automated

unit tests that detect problems in your code.

Mocha is one of the most used JavaScript testing frameworks.

It runs on Node and in the browser.

Mocha is a flexible and

extendable library that provides the base structure for setting up your tests.

It can be easily integrated with other testing libraries for

additional functionality, too.

And Jasmine is another popular JavaScript unit testing framework.

The good thing is that Jasmine does not depend on any other JavaScript framework.

It comes batteries included,

providing everything you need to test your code right out of the box.

It's also the popular choice for testing angular applications.

It makes testing much easier to set up and run.

And Jest is a feature-rich testing library created by Facebook.

Many React developers test with Jest

because it's already set up when you create a project with Create React App.

But you can test any JavaScript application with Jest.

It's built for unit and integration testing, which means that it can run tests

that check if all the units of your app work together correctly.

And Enzyme is a JavaScript testing utility for React, created and used by Airbnb.

It's also built to be compatible with other testing libraries.

Writing unit test can help you improve your code,

before you even start writing it, and can serve as valuable documentation for

how your application is supposed to work.

You'll have your bugs, spend less time debugging, and

a better understand the problems you do have.

As JavaScript developer Eric Elliott stated, tests are your first and

best line of defense against software defects.