babel-plugin-tester

12.0.0 verified Sat Apr 25 auth: no javascript

Utilities for writing tests for Babel plugins and presets. Version 12.0.0 is current. The library supports Jest, Mocha, Jasmine, node:test, and Vitest. Key differentiators: automatic fixture file loading, built-in prettier formatting, snapshot-based testing, environment variable filtering (TEST_ONLY, TEST_SKIP), and async ResultFormatter. Breaking changes in v12 include dropping default exports, requiring Node.js >=20.18.0, and adopting prettier@3's async interface. Peer dependency on @babel/core >=7.22.0.

Common errors

error TypeError: pluginTester is not a function ↓

cause Using default import with v12+ which removed default export.

fix

Change to named import: import { pluginTester } from 'babel-plugin-tester'

error Error: Cannot find module 'babel-plugin-tester' ↓

cause Missing install or wrong import path.

fix

Run npm install --save-dev babel-plugin-tester and ensure import path is correct.

error AssertionError: expected 'const x = 1;' to equal 'const x = 2;' ↓

cause Test output mismatch; plugin may not be transforming as expected.

fix

Check plugin logic and verify test input/output.

Warnings

breaking Default export removed in v12. Import { pluginTester } instead of default import. ↓

fix Change `import pluginTester from 'babel-plugin-tester'` to `import { pluginTester } from 'babel-plugin-tester'`.

breaking Minimum Node.js version is now 20.18.0 (v12). ↓

fix Upgrade Node.js to >=20.18.0.

breaking ResultFormatter is now async (returns Promise) due to prettier@3. ↓

fix If using custom formatter, ensure it returns a Promise or use async/await.

gotcha With prettier@3, some Node versions require --experimental-vm-modules flag. ↓

fix Run tests with `NODE_OPTIONS='--no-warnings --experimental-vm-modules' npx jest`.

breaking Implicit global option merging removed in v11. All options must be explicitly set per test or via global config. ↓

fix Move shared options to the top-level pluginTester configuration.

Install

npm install babel-plugin-tester

yarn add babel-plugin-tester

pnpm add babel-plugin-tester

Imports

pluginTester

wrong

import pluginTester from 'babel-plugin-tester'

correct

import { pluginTester } from 'babel-plugin-tester'

Default export was removed in v12. Use named import only.

prettierFormatter
```
import { prettierFormatter } from 'babel-plugin-tester'
```
Available as a named export; commonly used to format output with Prettier.
pluginTester (CJS)
wrong
```
const pluginTester = require('babel-plugin-tester')
```
correct
```
const { pluginTester } = require('babel-plugin-tester')
```
CJS require must destructure the named export. Default require returns an object with named exports.

Quickstart

Basic test suite for a Babel plugin with inline code tests and a snapshot test.

import { pluginTester } from 'babel-plugin-tester';
import myPlugin from './my-plugin';

pluginTester({
  plugin: myPlugin,
  tests: {
    'transforms correctly': {
      code: 'const x = 1;',
      output: 'const x = 1;',
    },
    'snapshot test': {
      code: 'const y = 2;',
      snapshot: true,
    },
  },
});