Write your first tests with Node's built-in test runner

You want to prove your code works before you touch it again, but adding a testing framework feels like a whole project on its own.

Beginner to intermediateRead 5 minDoing: about 30 minutes6 steps

▶ Start

What you'll have at the end

A test file that runs with node --test and fails on purpose once, then passes

Before you start

You need

A small function already written in your own Node project, with at least one input whose correct answer you have worked out by hand, and a package manifest already in the same folder.

Not covered

Testing code that waits on a network call or a database, and the mocking tools the same runner provides for that, which is a separate skill built on top of this one.

Leans on

6 steps

Where to go next

Debug a running Node process with breakpoints and the inspector

when a failing assertion's own diff isn't enough to tell you why a value is wrong, and you need to step through the code that produced it.

Checked 25 Aug 2026

Part of the Node.js cookbook