feat(config): add defineConfig and mergeConfig functions

Author: ahnpnl

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## main
 
+### Features
+
+- `[jest-config]` Add `defineConfig` and `mergeConfig` helpers for type-safe Jest config ([#15844](https://github.com/jestjs/jest/pull/15844))
+
 ## 30.2.0
 
 ### Chore & Maintenance

e2e/__tests__/config.test.ts

@@ -75,3 +75,48 @@ test('negated flags override previous flags', () => {
 
   expect(globalConfig.silent).toBe(true);
 });
+
+test('should work with define config function taking in config object', () => {
+  const result = runJest('config-utils', [
+    '--config=jest.config.ts',
+    '__tests__/simple.test.js',
+  ]);
+
+  expect(result.exitCode).toBe(0);
+});
+
+test('should work with define config function taking in callback', () => {
+  const result = runJest('config-utils', [
+    '--config=jest.callback.config.ts',
+    '__tests__/simple.test.js',
+  ]);
+
+  expect(result.exitCode).toBe(0);
+});
+
+test('should work with merged config of 2 config objects', () => {
+  const result = runJest('config-utils', [
+    '--config=jest.merge.config.ts',
+    '__tests__/merge.test.js',
+  ]);
+
+  expect(result.exitCode).toBe(0);
+});
+
+test('should work with merged config of one config object with a define function config', () => {
+  const result = runJest('config-utils', [
+    '--config=jest.merge-with-define.config.ts',
+    '__tests__/merge.test.js',
+  ]);
+
+  expect(result.exitCode).toBe(0);
+});
+
+test('should work with merged config as callback for define function config', () => {
+  const result = runJest('config-utils', [
+    '--config=jest.merge-with-callback.config.ts',
+    '__tests__/merge.test.js',
+  ]);
+
+  expect(result.exitCode).toBe(0);
+});

e2e/config-utils/__tests__/merge.test.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('should work', () => {
+  expect(typeof globalThis.window).toBe('object');
+  expect(1 + 1).toBe(2);
+});

e2e/config-utils/__tests__/simple.test.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('should work', () => {
+  expect(1 + 1).toBe(2);
+});

e2e/config-utils/jest.callback.config.ts

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @jest-config-loader esbuild-register
+ */
+
+import {type Config, defineConfig} from 'jest';
+
+export default defineConfig(async () => {
+  const baseConfig = await new Promise<Config>(resolve => {
+    setTimeout(() => {
+      resolve({
+        testEnvironment: 'node',
+      });
+    });
+  });
+
+  return {
+    ...baseConfig,
+    displayName: 'callback-config',
+  };
+});

e2e/config-utils/jest.config.ts

@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @jest-config-loader esbuild-register
+ */
+
+import {defineConfig} from 'jest';
+
+export default defineConfig({
+  displayName: 'simple-config',
+  testEnvironment: 'node',
+});

e2e/config-utils/jest.merge-with-callback.config.ts

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @jest-config-loader esbuild-register
+ */
+
+import {defineConfig, mergeConfig} from 'jest';
+import jestConfig from './jest.config';
+
+export default defineConfig(() =>
+  mergeConfig(
+    jestConfig,
+    defineConfig({
+      displayName: 'merge-with-callback',
+      testEnvironment: 'jsdom',
+    }),
+  ),
+);

e2e/config-utils/jest.merge-with-define.config.ts

@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @jest-config-loader esbuild-register
+ */
+
+import {defineConfig, mergeConfig} from 'jest';
+import jestConfig from './jest.config';
+
+export default mergeConfig(
+  jestConfig,
+  defineConfig({
+    displayName: 'merge-with-define-config',
+    testEnvironment: 'jsdom',
+  }),
+);

e2e/config-utils/jest.merge.config.ts

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @jest-config-loader esbuild-register
+ */
+
+import {mergeConfig} from 'jest';
+import baseConfig from './jest.config';
+
+export default mergeConfig(baseConfig, {
+  displayName: 'merge-config',
+  testEnvironment: 'jsdom',
+});

e2e/config-utils/package.json

@@ -0,0 +1,5 @@
+{
+  "jest": {
+    "testEnvironment": "node"
+  }
+}