feat(babel-jest): add option excludeJestPreset (#15164)

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[babel-jest]` Add option `excludeJestPreset` to allow opting out of `babel-preset-jest` ([#15164](https://github.com/jestjs/jest/pull/15164))
 - `[jest-circus, jest-cli, jest-config]` Add `waitNextEventLoopTurnForUnhandledRejectionEvents` flag to minimise performance impact of correct detection of unhandled promise rejections introduced in [#14315](https://github.com/jestjs/jest/pull/14315) ([#14681](https://github.com/jestjs/jest/pull/14681))
 - `[jest-circus]` Add a `waitBeforeRetry` option to `jest.retryTimes` ([#14738](https://github.com/jestjs/jest/pull/14738))
 - `[jest-circus]` Add a `retryImmediately` option to `jest.retryTimes` ([#14696](https://github.com/jestjs/jest/pull/14696))

docs/CodeTransformation.md

@@ -15,6 +15,18 @@ Jest will cache the result of a transformation and attempt to invalidate that re
 
 Jest ships with one transformer out of the box – [`babel-jest`](https://github.com/jestjs/jest/tree/main/packages/babel-jest#setup). It will load your project's Babel configuration and transform any file matching the `/\.[jt]sx?$/` RegExp (in other words, any `.js`, `.jsx`, `.ts` or `.tsx` file). In addition, `babel-jest` will inject the Babel plugin necessary for mock hoisting talked about in [ES Module mocking](ManualMocks.md#using-with-es-module-imports).
 
+:::note
+
+By default, `babel-jest` includes `babel-preset-jest`. You can disable this behavior by specifying `excludeJestPreset: true` to `babel-jest`. Note that this will also stop hoisting `jest.mock`, which may break your tests.
+
+```json
+"transform": {
+  "\\.[jt]sx?$": ["babel-jest", { "excludeJestPreset": true }],
+}
+```
+
+:::
+
 :::tip
 
 Remember to include the default `babel-jest` transformer explicitly, if you wish to use it alongside with additional code preprocessors:

packages/babel-jest/README.md

@@ -33,3 +33,11 @@ You can also pass further [babel options](https://babeljs.io/docs/options)
   "\\.[jt]sx?$": ["babel-jest", { "extends": "./babel.config.js", "plugins": ["babel-plugin-transform-import-meta"] }]
 },
 ```
+
+By default, `babel-jest` includes `babel-preset-jest`. In addition to the babel options, we introduce a new option, `excludeJestPreset`, which allows you to disable this behavior. Note that this will break `jest.mock` hoisting.
+
+```json
+"transform": {
+  "\\.[jt]sx?$": ["babel-jest", { "excludeJestPreset": true }],
+}
+```

packages/babel-jest/src/__tests__/index.ts

@@ -169,3 +169,34 @@ test('can pass null to createTransformer', async () => {
     }),
   );
 });
+
+test('include babel-preset-jest by default', () => {
+  defaultBabelJestTransformer.process(sourceString, 'dummy_path.js', {
+    cacheFS: new Map<string, string>(),
+    config: makeProjectConfig(),
+    configString: JSON.stringify(makeProjectConfig()),
+    instrument: false,
+    transformerConfig: {},
+  } as TransformOptions<BabelTransformOptions>);
+
+  expect(loadPartialConfig).toHaveBeenCalledTimes(1);
+  expect(loadPartialConfig).toHaveBeenCalledWith(
+    expect.objectContaining({presets: [require.resolve('babel-preset-jest')]}),
+  );
+});
+
+test('can opting out of babel-preset-jest by passing excludeJestPreset: true', async () => {
+  const transformer = await createTransformer({excludeJestPreset: true});
+  transformer.process(sourceString, 'dummy_path.js', {
+    cacheFS: new Map<string, string>(),
+    config: makeProjectConfig(),
+    configString: JSON.stringify(makeProjectConfig()),
+    instrument: false,
+    transformerConfig: {},
+  } as TransformOptions<BabelTransformOptions>);
+
+  expect(loadPartialConfig).toHaveBeenCalledTimes(1);
+  expect(loadPartialConfig).toHaveBeenCalledWith(
+    expect.objectContaining({presets: []}),
+  );
+});

packages/babel-jest/src/index.ts

@@ -8,8 +8,8 @@
 import {createHash} from 'crypto';
 import * as path from 'path';
 import {
+  type TransformOptions as BabelTransformOptions,
   type PartialConfig,
-  type TransformOptions,
   transformSync as babelTransform,
   transformAsync as babelTransformAsync,
 } from '@babel/core';
@@ -23,6 +23,10 @@ import type {
 } from '@jest/transform';
 import {loadPartialConfig, loadPartialConfigAsync} from './loadBabelConfig';
 
+interface TransformerConfig extends BabelTransformOptions {
+  excludeJestPreset?: boolean;
+}
+
 const THIS_FILE = fs.readFileSync(__filename);
 const jestPresetPath = require.resolve('babel-preset-jest');
 const babelIstanbulPlugin = require.resolve('babel-plugin-istanbul');
@@ -44,11 +48,11 @@ function assertLoadedBabelConfig(
 }
 
 function addIstanbulInstrumentation(
-  babelOptions: TransformOptions,
+  babelOptions: BabelTransformOptions,
   transformOptions: JestTransformOptions,
-): TransformOptions {
+): BabelTransformOptions {
   if (transformOptions.instrument) {
-    const copiedBabelOptions: TransformOptions = {...babelOptions};
+    const copiedBabelOptions: BabelTransformOptions = {...babelOptions};
     copiedBabelOptions.auxiliaryCommentBefore = ' istanbul ignore next ';
     // Copied from jest-runtime transform.js
     copiedBabelOptions.plugins = [
@@ -106,7 +110,7 @@ function getCacheKeyFromConfig(
 function loadBabelConfig(
   cwd: string,
   filename: string,
-  transformOptions: TransformOptions,
+  transformOptions: BabelTransformOptions,
 ): PartialConfig {
   const babelConfig = loadPartialConfig(transformOptions);
 
@@ -118,7 +122,7 @@ function loadBabelConfig(
 async function loadBabelConfigAsync(
   cwd: string,
   filename: string,
-  transformOptions: TransformOptions,
+  transformOptions: BabelTransformOptions,
 ): Promise<PartialConfig> {
   const babelConfig = await loadPartialConfigAsync(transformOptions);
 
@@ -130,9 +134,9 @@ async function loadBabelConfigAsync(
 function loadBabelOptions(
   cwd: string,
   filename: string,
-  transformOptions: TransformOptions,
+  transformOptions: BabelTransformOptions,
   jestTransformOptions: JestTransformOptions,
-): TransformOptions {
+): BabelTransformOptions {
   const {options} = loadBabelConfig(cwd, filename, transformOptions);
 
   return addIstanbulInstrumentation(options, jestTransformOptions);
@@ -141,19 +145,19 @@ function loadBabelOptions(
 async function loadBabelOptionsAsync(
   cwd: string,
   filename: string,
-  transformOptions: TransformOptions,
+  transformOptions: BabelTransformOptions,
   jestTransformOptions: JestTransformOptions,
-): Promise<TransformOptions> {
+): Promise<BabelTransformOptions> {
   const {options} = await loadBabelConfigAsync(cwd, filename, transformOptions);
 
   return addIstanbulInstrumentation(options, jestTransformOptions);
 }
 
 export const createTransformer: TransformerCreator<
-  SyncTransformer<TransformOptions>,
-  TransformOptions
-> = userOptions => {
-  const inputOptions = userOptions ?? {};
+  SyncTransformer<TransformerConfig>,
+  TransformerConfig
+> = transformerConfig => {
+  const {excludeJestPreset, ...inputOptions} = transformerConfig ?? {};
 
   const options = {
     ...inputOptions,
@@ -167,14 +171,17 @@ export const createTransformer: TransformerCreator<
     },
     compact: false,
     plugins: inputOptions.plugins ?? [],
-    presets: [...(inputOptions.presets ?? []), jestPresetPath],
+    presets: [
+      ...(inputOptions.presets ?? []),
+      ...(excludeJestPreset === true ? [] : [jestPresetPath]),
+    ],
     sourceMaps: 'both',
-  } satisfies TransformOptions;
+  } satisfies BabelTransformOptions;
 
   function mergeBabelTransformOptions(
     filename: string,
     transformOptions: JestTransformOptions,
-  ): TransformOptions {
+  ): BabelTransformOptions {
     const {cwd, rootDir} = transformOptions.config;
     // `cwd` and `root` first to allow incoming options to override it
     return {