# Testing with node:test — Node.js Fundamentals: Modules, Async and Servers

Source: https://www.geekswithgeeks.com/en/nodejs/node-test-runner

> Write and run unit tests with Node's built-in test runner and the assert module, with no extra dependencies.

## The built-in test runner

Since Node 20 the test runner is stable. Import `test` from `node:test` and use `node:assert` for checks.

```javascript
// add.test.js
import test from "node:test";
import assert from "node:assert/strict";
import { add } from "./math.js";

test("adds two numbers", () => {
  assert.equal(add(2, 3), 5);
});

test("async works", async () => {
  const data = await Promise.resolve(42);
  assert.equal(data, 42);
});
```

Run all test files, watch for changes and collect coverage.

```bash
node --test
node --test --watch
node --test --experimental-test-coverage
```

Keep tests small and independent, name them after the behaviour, and run them in CI on every push.

Quick check

**Quiz:** Which command runs Node's built-in tests?

- [x] node --test
- [ ] npm install test
- [ ] node --check
- [ ] node --lint

*Answer:* node --test. `node --test` discovers and runs test files with the built-in runner.