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Yes, Node.js has a built-in test runner. Run node --test in a project and Node finds matching test files, runs them, and reports results. You define tests with the node:test module. You don’t install a separate runner package. This guide covers the first test, how files are discovered, process isolation, and the extras (watch mode, coverage, mocking). It also gives the stability label for each extra, because those labels vary by release.
Write and run your first test
The Node.js documentation describes the runner this way: “The Node.js test runner can be invoked from the command line by passing the --test flag.” The tests themselves come from the node:test module, and assertions come from node:assert. Both ship with Node.
Create a file named math.test.js:
import test from 'node:test';
import assert from 'node:assert';
test('adds two numbers', () => {
assert.strictEqual(1 + 2, 3);
});Then run:
node --testNode discovers the file, runs it, and prints a result for each test. A test passes if its function returns without throwing. A failed assertion throws, so the test fails. The example uses ES module import syntax. In a CommonJS project, use require('node:test') and require('node:assert') instead.
How Node finds your test files
Not every .js file counts as a test. Without arguments, the runner looks for files matching documented naming patterns. The current documentation lists these:
example.test.jsexample-test.jsexample_test.jstest-example.jstest.js- files under a
test/directory
The documentation also covers TypeScript extensions when type stripping is in effect. Passing --no-strip-types changes that behavior.
Choosing files yourself
To override the defaults, pass explicit glob patterns. Quote them so your shell doesn’t expand them before Node sees them:
node --test "src/**/*.spec.js"This is the fix when your naming convention doesn’t match the defaults, or when you want to run one slice of the suite.
Process isolation: why files don’t share state
By default, each matching file runs in its own child process. Files therefore don’t normally share one JavaScript global context. A global variable or a patched built-in in one file won’t leak into another.
Rank #3
- Concurrency: the
--test-concurrencyflag controls how many child processes run at once. - Turning isolation off: if you disable process isolation, files share a context. Global state can then cause cross-file interference, so only do it if your tests are written with that in mind.
Useful features beyond the basics
| Feature | How to use it | Stability label in the v26.8.2 docs |
|---|---|---|
| Watch mode | node --test --watch |
Experimental |
| Coverage | node --test --experimental-test-coverage |
Experimental |
| Mocking | Provided by the node:test API |
Not stated in the material reviewed |
| Global setup/teardown | Documented as added in v24.0.0 | Early development |
Watch mode
The documentation says: “In watch mode, the test runner will watch for changes to test files and their dependencies.” Edit a file and the affected tests rerun, which suits a tight edit-and-test loop.
Coverage
Add --experimental-test-coverage to get a coverage report with your test results. The flag name itself carries the experimental label.
Mocking
The node:test module includes mocking support, so you can replace functions or methods during a test without a separate mocking library. See the Test runner page for your Node version for the exact API.
Global setup and teardown
This appears in the v26.8.2 documentation as added in v24.0.0 and is labeled early development. Don’t rely on it in older releases, and expect it to change.
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Check your Node version
Flags, defaults and stability labels differ between releases. The details above come from the Node.js v26.8.2 Test runner documentation. Run node --version, then read the Test runner page for that version at nodejs.org before depending on an experimental flag or a feature added recently. This page doesn’t compare the built-in runner with third-party frameworks. Whether it replaces one in your project depends on the integrations and features you need.
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