Javascript Testing Tools Explained: What Beginners Really Need To Know

If you just learned what testing is and you’re still a bit unsure how to start, you’re not alone. Many beginner developers feel overwhelmed by the amount of tools and libraries in the Javascript testing world. You might wonder: do I need Jest? What is Vitest? Why does everyone keep talking about mocking things?

Let me help you make sense of it all.

This post builds on the one you (hopefully) already read: Javascript testing for beginners: A simple, practical introduction. If not, it’s a good starting point to understand why testing matters in the first place. Here, we’ll talk about what tools are out there, why they exist, and how to choose the right one for your project.

Why so many testing tools?

The short answer is: because testing needs can be very different. Some developers need to test just one small function. Others need to simulate how a user clicks buttons on a real webpage. Some need to test backend logic or APIs. And some want all of that together.

Different tools are created to solve different testing problems. Let’s look at the main ones you’ll hear about.

What is a testing framework?

Before going further, let’s clear something up. When people say “testing framework” or “testing library,” they sometimes mix up terms. In this post, we’ll use them loosely. Don’t worry too much about definitions.

But just so we’re on the same page:

• A testing framework usually provides the structure: how to describe a test, run it, and report results.
• A testing library might focus on one specific part of the testing process (like simulating user actions or helping with mocking).

Now let’s see what each popular tool actually does.

Jest: The default for many projects

Jest is probably the first tool you’ll hear about in Javascript testing. It’s widely used, especially in React projects. And for good reason—it comes with most things you need built in: test runner, assertion library, and mocking tools.

• You can write simple tests using test() and expect().
• You can mock functions easily (see what a mock is if you’re unsure).
• It works out of the box with many setups.

A basic test in Jest looks like this:

import { sum } from './math';

test('adds two numbers', () => {
  expect(sum(2, 3)).toBe(5);
});

import { sum } from './math';

test('adds two numbers', () => {
  expect(sum(2, 3)).toBe(5);
});

Jest is great for unit tests, which are explained more deeply in Integration and unit tests: How to choose the right one?. But it also supports more advanced setups.

Still, Jest isn’t perfect for every case.

Vitest: Fast and Vite-Friendly

If you’re using Vite, you might prefer Vitest. It’s a newer test runner that works very similarly to Jest but is built for speed and modern dev setups.

It supports:

• ES modules by default
• Fast startup thanks to Vite integration
• Very similar API to Jest, so switching isn’t too hard

If you’re just starting and you already use Vite for your project, Vitest is a great alternative. It feels lighter and quicker, especially for frontend apps.

Testing Library (RTL): For testing UI like a real user

React Testing Library (often called RTL) is a library for testing user interfaces. It doesn’t replace Jest—it works with Jest.

RTL helps you simulate how users actually interact with your app:

• Clicking buttons
• Typing in inputs
• Checking if the right text shows up

Instead of testing if a certain component method was called, you test what the user sees. This makes your tests more realistic.

It follows a rule: “The more your tests resemble the way your software is used, the more confidence they can give you.”

Mocha, Chai, Sinon: The Classic Trio

Before Jest became popular, many Javascript projects used this combo:

• Mocha for running tests
• Chai for writing assertions
• Sinon for creating mocks and spies

These tools are still good and used in some backend or legacy projects. They give you more flexibility, but also more setup.

For example, to run tests with Mocha and Chai, you’ll usually need to install them separately and configure them more manually.

If you’re just starting, you don’t need to go this route unless you’re joining a project that already uses them.

What about Mocks, Spies, and Stubs?

You’ll hear these words a lot when testing. Here’s what they mean in simple terms:

• A mock is a fake function that replaces a real one during testing. It lets you test what happens without calling the real thing.
• A spy is a function that records if and how it was called, but still lets the real function run.
• A stub is like a mock but with more control—you can decide what it returns.

If you’re confused, check the glossary entries for mock and spy.

These tools are helpful in unit testing, when you want to isolate just one part of your code. For example, you might want to check that a function called another one, but without actually doing what the second one does.

What should you use as a beginner?

Here’s a simple suggestion:

• Start with Jest. It’s well-documented, easy to set up, and covers most use cases.
• If you’re using Vite, try Vitest instead.
• If you’re building user interfaces, add Testing Library to test what the user sees.

You don’t need everything at once. Focus on learning how to write a few tests. You’ll naturally learn the tools better as you write more code.

A quick example: Putting it together

Let’s say you have a small function like this:

export function greetUser(name) {
  return `Hello, ${name}!`;
}

export function greetUser(name) {
  return `Hello, ${name}!`;
}

A simple unit test using Vitest would be:

import { describe, it, expect } from 'vitest';
import { greetUser } from './greet';

describe('greetUser', () => {
  it('greets by name', () => {
    expect(greetUser('Anna')).toBe('Hello, Anna!');
  });
});

import { describe, it, expect } from 'vitest';
import { greetUser } from './greet';

describe('greetUser', () => {
  it('greets by name', () => {
    expect(greetUser('Anna')).toBe('Hello, Anna!');
  });
});

You could use Jest instead—the code would almost be the same. This test checks the return value, no mocking needed.

Later, if your function becomes more complex (calls an API, uses another function), you might use a mock to isolate the behavior. You can then write more detailed tests, like we discuss in Integration and unit tests: How to choose the right one?.

Final thoughts

Don’t feel like you need to master every testing tool at once. Testing is a skill you build slowly. Start small, use a simple tool like Jest or Vitest, and practice writing real tests.

If you’re ever stuck on what kind of test to write, go back to Javascript testing for beginners and Integration and unit tests: How to choose the right one? to refresh the theory.

The tools are just tools—they’re here to help you write better, safer code. And soon, you’ll start to feel that they do.