feat: Add support for the jest.config.ts configuration file

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+- `[jest-cli, jest-config]` Add support for the `jest.config.ts` configuration file ([#10564](https://github.com/facebook/jest/pull/10564))
+
 ### Fixes
 
 ### Chore & Maintenance

docs/Configuration.md

@@ -3,7 +3,7 @@ id: configuration
 title: Configuring Jest
 ---
 
-Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js` file or through the `--config <path/to/file.js|cjs|mjs|json>` option. If you'd like to use your `package.json` to store Jest's config, the `"jest"` key should be used on the top level so Jest will know how to find your settings:
+Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js`, or `jest.config.ts` file or through the `--config <path/to/file.js|ts|cjs|mjs|json>` option. If you'd like to use your `package.json` to store Jest's config, the `"jest"` key should be used on the top level so Jest will know how to find your settings:
 
 ```json
 {
@@ -18,19 +18,39 @@ Or through JavaScript:
 
 ```js
 // jest.config.js
-//Sync object
+// Sync object
 module.exports = {
   verbose: true,
 };
 
-//Or async function
+// Or async function
 module.exports = async () => {
   return {
     verbose: true,
   };
 };
 ```
 
+Or through TypeScript (if `ts-node` is installed):
+
+```ts
+// jest.config.ts
+import type {Config} from '@jest/types';
+
+// Sync object
+const config: Config.InitialOptions = {
+  verbose: true,
+};
+export default config;
+
+// Or async function
+export default async (): Promise<Config.InitialOptions> => {
+  return {
+    verbose: true,
+  };
+};
+```
+
 Please keep in mind that the resulting configuration must be JSON-serializable.
 
 When using the `--config` option, the JSON file must not contain a "jest" key:

e2e/__tests__/__snapshots__/jest.config.ts.test.ts.snap

@@ -0,0 +1,36 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`traverses directory tree up until it finds jest.config 1`] = `
+  console.log
+<<REPLACED>>/jest.config.ts/some/nested/directory
+
+      at Object.log (__tests__/a-giraffe.js:3:27)
+
+`;
+
+exports[`traverses directory tree up until it finds jest.config 2`] = `
+PASS ../../../__tests__/a-giraffe.js
+  ✓ giraffe
+  ✓ abc
+`;
+
+exports[`traverses directory tree up until it finds jest.config 3`] = `
+Test Suites: 1 passed, 1 total
+Tests:       2 passed, 2 total
+Snapshots:   0 total
+Time:        <<REPLACED>>
+Ran all test suites.
+`;
+
+exports[`works with jest.config.ts 1`] = `
+PASS __tests__/a-giraffe.js
+  ✓ giraffe
+`;
+
+exports[`works with jest.config.ts 2`] = `
+Test Suites: 1 passed, 1 total
+Tests:       1 passed, 1 total
+Snapshots:   0 total
+Time:        <<REPLACED>>
+Ran all test suites.
+`;

e2e/__tests__/jest.config.ts.test.ts

@@ -0,0 +1,83 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import * as path from 'path';
+import {wrap} from 'jest-snapshot-serializer-raw';
+import runJest from '../runJest';
+import {cleanup, extractSummary, writeFiles} from '../Utils';
+
+const DIR = path.resolve(__dirname, '../jest.config.ts');
+
+beforeEach(() => cleanup(DIR));
+afterAll(() => cleanup(DIR));
+
+test('works with jest.config.ts', () => {
+  writeFiles(DIR, {
+    '__tests__/a-giraffe.js': `test('giraffe', () => expect(1).toBe(1));`,
+    'jest.config.ts': `export default {testEnvironment: 'jest-environment-node', testRegex: '.*-giraffe.js'};`,
+    'package.json': '{}',
+  });
+
+  const {stderr, exitCode} = runJest(DIR, ['-w=1', '--ci=false']);
+  const {rest, summary} = extractSummary(stderr);
+  expect(exitCode).toBe(0);
+  expect(wrap(rest)).toMatchSnapshot();
+  expect(wrap(summary)).toMatchSnapshot();
+});
+
+test('traverses directory tree up until it finds jest.config', () => {
+  writeFiles(DIR, {
+    '__tests__/a-giraffe.js': `
+    const slash = require('slash');
+    test('giraffe', () => expect(1).toBe(1));
+    test('abc', () => console.log(slash(process.cwd())));
+    `,
+    'jest.config.ts': `export default {testEnvironment: 'jest-environment-node', testRegex: '.*-giraffe.js'};`,
+    'package.json': '{}',
+    'some/nested/directory/file.js': '// nothing special',
+  });
+
+  const {stderr, exitCode, stdout} = runJest(
+    path.join(DIR, 'some', 'nested', 'directory'),
+    ['-w=1', '--ci=false'],
+    {skipPkgJsonCheck: true},
+  );
+
+  // Snapshot the console.loged `process.cwd()` and make sure it stays the same
+  expect(
+    wrap(stdout.replace(/^\W+(.*)e2e/gm, '<<REPLACED>>')),
+  ).toMatchSnapshot();
+
+  const {rest, summary} = extractSummary(stderr);
+  expect(exitCode).toBe(0);
+  expect(wrap(rest)).toMatchSnapshot();
+  expect(wrap(summary)).toMatchSnapshot();
+});
+
+test('it does type check the config', () => {
+  writeFiles(DIR, {
+    '__tests__/a-giraffe.js': `test('giraffe', () => expect(1).toBe(1));`,
+    'jest.config.ts': `export default { testTimeout: "10000" }`,
+    'package.json': '{}',
+  });
+
+  const {stderr, exitCode} = runJest(DIR, ['-w=1', '--ci=false']);
+  expect(stderr).toMatch('must be of type');
+  expect(exitCode).toBe(1);
+});
+
+test('invalid JS in jest.config.ts', () => {
+  writeFiles(DIR, {
+    '__tests__/a-giraffe.js': `test('giraffe', () => expect(1).toBe(1));`,
+    'jest.config.ts': `export default i'll break this file yo`,
+    'package.json': '{}',
+  });
+
+  const {stderr, exitCode} = runJest(DIR, ['-w=1', '--ci=false']);
+  expect(stderr).toMatch('TSError: ⨯ Unable to compile TypeScript:');
+  expect(exitCode).toBe(1);
+});

package.json

@@ -77,6 +77,7 @@
     "strip-ansi": "^6.0.0",
     "tempy": "^0.6.0",
     "throat": "^5.0.0",
+    "ts-node": "^9.0.0",
     "type-fest": "^0.16.0",
     "typescript": "^4.0.2",
     "which": "^2.0.1"

packages/jest-cli/src/__tests__/cli/args.test.ts

@@ -82,13 +82,13 @@ describe('check', () => {
   it('raises an exception if config is not a valid JSON string', () => {
     const argv = {config: 'x:1'} as Config.Argv;
     expect(() => check(argv)).toThrow(
-      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .mjs, .cjs, .json',
+      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .ts, .mjs, .cjs, .json',
     );
   });
 
   it('raises an exception if config is not a supported file type', () => {
     const message =
-      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .mjs, .cjs, .json';
+      'The --config option requires a JSON string literal, or a file path with one of these extensions: .js, .ts, .mjs, .cjs, .json';
 
     expect(() => check({config: 'jest.configjs'} as Config.Argv)).toThrow(
       message,

packages/jest-cli/src/init/__tests__/__snapshots__/init.test.js.snap

@@ -45,9 +45,81 @@ Object {
 }
 `;
 
+exports[`init has-jest-config-file-ts ask the user whether to override config or not user answered with "Yes" 1`] = `
+Object {
+  "initial": true,
+  "message": "It seems that you already have a jest configuration, do you want to override it?",
+  "name": "continue",
+  "type": "confirm",
+}
+`;
+
+exports[`init project using jest.config.ts ask the user whether he wants to use Typescript or not user answered with "Yes" 1`] = `
+Array [
+  Object {
+    "initial": true,
+    "message": "Would you like to use Jest when running \\"test\\" script in \\"package.json\\"?",
+    "name": "scripts",
+    "type": "confirm",
+  },
+  Object {
+    "initial": false,
+    "message": "Would you like to use Typescript for the configuration file?",
+    "name": "useTypescript",
+    "type": "confirm",
+  },
+  Object {
+    "choices": Array [
+      Object {
+        "title": "node",
+        "value": "node",
+      },
+      Object {
+        "title": "jsdom (browser-like)",
+        "value": "jsdom",
+      },
+    ],
+    "initial": 0,
+    "message": "Choose the test environment that will be used for testing",
+    "name": "environment",
+    "type": "select",
+  },
+  Object {
+    "initial": false,
+    "message": "Do you want Jest to add coverage reports?",
+    "name": "coverage",
+    "type": "confirm",
+  },
+  Object {
+    "choices": Array [
+      Object {
+        "title": "v8",
+        "value": "v8",
+      },
+      Object {
+        "title": "babel",
+        "value": "babel",
+      },
+    ],
+    "initial": 0,
+    "message": "Which provider should be used to instrument code for coverage?",
+    "name": "coverageProvider",
+    "type": "select",
+  },
+  Object {
+    "initial": false,
+    "message": "Automatically clear mock calls and instances between every test?",
+    "name": "clearMocks",
+    "type": "confirm",
+  },
+]
+`;
+
 exports[`init project with package.json and no jest config all questions answered with answer: "No" should return the default configuration (an empty config) 1`] = `
-"// For a detailed explanation regarding each configuration property, visit:
-// https://jestjs.io/docs/en/configuration.html
+"/*
+ * For a detailed explanation regarding each configuration property, visit:
+ * https://jestjs.io/docs/en/configuration.html
+ */
 
 module.exports = {
   // All imported modules in your tests should be mocked automatically

packages/jest-cli/src/init/__tests__/fixtures/has_jest_config_file_ts/jest.config.ts

@@ -0,0 +1,8 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+export default {};

packages/jest-cli/src/init/__tests__/fixtures/has_jest_config_file_ts/package.json

@@ -0,0 +1 @@
+{}

packages/jest-cli/src/init/__tests__/fixtures/test_generated_jest_config_ts/package.json

@@ -0,0 +1 @@
+{}

packages/jest-cli/src/init/__tests__/init.test.js

@@ -66,7 +66,7 @@ describe('init', () => {
         expect(writtenJestConfigFilename.endsWith('.mjs')).toBe(true);
 
         expect(typeof writtenJestConfig).toBe('string');
-        expect(writtenJestConfig.split('\n')[3]).toBe('export default {');
+        expect(writtenJestConfig.split('\n')[5]).toBe('export default {');
       });
     });
 
@@ -193,6 +193,34 @@ describe('init', () => {
     },
   );
 
+  describe('project using jest.config.ts', () => {
+    describe('ask the user whether he wants to use Typescript or not', () => {
+      it('user answered with "Yes"', async () => {
+        prompts.mockReturnValueOnce({useTypescript: true});
+
+        await init(resolveFromFixture('test_generated_jest_config_ts'));
+
+        expect(prompts.mock.calls[0][0]).toMatchSnapshot();
+
+        const jestConfigFileName = fs.writeFileSync.mock.calls[0][0];
+        const writtenJestConfig = fs.writeFileSync.mock.calls[0][1];
+
+        expect(jestConfigFileName).toContain('/jest.config.ts');
+        expect(writtenJestConfig.split('\n')[5]).toBe('export default {');
+      });
+
+      it('user answered with "No"', async () => {
+        prompts.mockReturnValueOnce({useTypescript: false});
+
+        await init(resolveFromFixture('test_generated_jest_config_ts'));
+
+        const jestConfigFileName = fs.writeFileSync.mock.calls[0][0];
+
+        expect(jestConfigFileName).not.toContain('jest.config.ts');
+      });
+    });
+  });
+
   describe('has jest config in package.json', () => {
     it('should ask the user whether to override config or not', async () => {
       prompts.mockReturnValueOnce({continue: true}).mockReturnValueOnce({});

packages/jest-cli/src/init/generate_config_file.ts

@@ -35,7 +35,13 @@ const generateConfigFile = (
   results: Record<string, unknown>,
   generateEsm = false,
 ): string => {
-  const {coverage, coverageProvider, clearMocks, environment} = results;
+  const {
+    useTypescript,
+    coverage,
+    coverageProvider,
+    clearMocks,
+    environment,
+  } = results;
 
   const overrides: Record<string, unknown> = {};
 
@@ -81,10 +87,20 @@ const generateConfigFile = (
     }
   }
 
+  const configHeaderMessage = `/*
+ * For a detailed explanation regarding each configuration property${
+   useTypescript ? ' and type check' : ''
+ }, visit:
+ * https://jestjs.io/docs/en/configuration.html
+ */
+
+`;
+
   return (
-    '// For a detailed explanation regarding each configuration property, visit:\n' +
-    '// https://jestjs.io/docs/en/configuration.html\n\n' +
-    (generateEsm ? 'export default {\n' : 'module.exports = {\n') +
+    configHeaderMessage +
+    (useTypescript || generateEsm
+      ? 'export default {\n'
+      : 'module.exports = {\n') +
     properties.join('\n') +
     '};\n'
   );