feat: allow reporters to be default exports

CHANGELOG.md

@@ -10,6 +10,7 @@
 - `[jest-config]` Throw the full error message and stack when a Jest preset is missing a dependency ([#8924](https://github.com/facebook/jest/pull/8924))
 - `[jest-config]` [**BREAKING**] Set default display name color based on runner ([#8689](https://github.com/facebook/jest/pull/8689))
 - `[jest-config]` Merge preset globals with project globals ([#9027](https://github.com/facebook/jest/pull/9027))
+- `[jest-core]` Support reporters as default exports ([#9161](https://github.com/facebook/jest/pull/9161))
 - `[jest-diff]` Add options for colors and symbols ([#8841](https://github.com/facebook/jest/pull/8841))
 - `[jest-diff]` [**BREAKING**] Export as ECMAScript module ([#8873](https://github.com/facebook/jest/pull/8873))
 - `[jest-diff]` Add `includeChangeCounts` and rename `Indicator` options ([#8881](https://github.com/facebook/jest/pull/8881))

docs/Configuration.md

@@ -627,6 +627,7 @@ class MyCustomReporter {
 }
 
 module.exports = MyCustomReporter;
+// or export default MyCustomReporter;
 ```
 
 Custom reporters can also force Jest to exit with non-0 code by returning an Error from `getLastError()` methods

e2e/__tests__/__snapshots__/customReporters.test.ts.snap

@@ -119,6 +119,13 @@ exports[`Custom Reporters Integration invalid format for adding reporters 1`] =
 
 `;
 
+exports[`Custom Reporters Integration reporters can be default exports 1`] = `
+run start
+test start
+test complete
+run complete
+`;
+
 exports[`Custom Reporters Integration valid array format for adding reporters 1`] = `
 {
     "onRunComplete": {

e2e/__tests__/customReporters.test.ts

@@ -121,6 +121,21 @@ describe('Custom Reporters Integration', () => {
     expect(wrap(stdout)).toMatchSnapshot();
   });
 
+  test('reporters can be default exports', () => {
+    const {stderr, stdout, exitCode} = runJest('custom-reporters', [
+      '--no-cache',
+      '--config',
+      JSON.stringify({
+        reporters: ['<rootDir>/reporters/DefaultExportReporter.js'],
+      }),
+      'add.test.js',
+    ]);
+
+    expect(stderr).toBe('');
+    expect(exitCode).toBe(0);
+    expect(wrap(stdout)).toMatchSnapshot();
+  });
+
   test('prints reporter errors', () => {
     writeFiles(DIR, {
       '__tests__/test.test.js': `test('test', () => {});`,

e2e/custom-reporters/reporters/DefaultExportReporter.js

@@ -0,0 +1,34 @@
+/**
+ * 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.
+ */
+
+// TODO: use babel to transpile actual import/export in Jest 26
+Object.defineProperty(exports, '__esModule', {
+  value: true,
+});
+exports.default = void 0;
+
+const _reporters = require('@jest/reporters');
+
+class TestReporter extends _reporters.BaseReporter {
+  onTestStart() {
+    console.log('test start');
+  }
+
+  onTestResult() {
+    console.log('test complete');
+  }
+
+  onRunStart() {
+    console.log('run start');
+  }
+
+  onRunComplete() {
+    console.log('run complete');
+  }
+}
+
+exports.default = TestReporter;

packages/jest-config/src/normalize.ts

@@ -393,7 +393,7 @@ const normalizeReporters = (options: Config.InitialOptionsWithRootDir) => {
         basedir: options.rootDir,
       });
       if (!reporter) {
-        throw new Error(
+        throw new Resolver.ModuleNotFoundError(
           `Could not resolve a module for a custom reporter.\n` +
             `  Module name: ${reporterPath}`,
         );

packages/jest-core/src/TestScheduler.ts

@@ -28,6 +28,7 @@ import {
   buildFailureTestResult,
   makeEmptyAggregatedTestResult,
 } from '@jest/test-result';
+import {interopRequireDefault} from 'jest-util';
 import ReporterDispatcher from './ReporterDispatcher';
 import TestWatcher from './TestWatcher';
 import {shouldRunInBand} from './testSchedulerHelper';
@@ -315,15 +316,16 @@ export default class TestScheduler {
       if (path === 'default') return;
 
       try {
-        const Reporter = require(path);
+        // TODO: Use `requireAndTranspileModule` for Jest 26
+        const Reporter = interopRequireDefault(require(path)).default;
         this.addReporter(new Reporter(this._globalConfig, options));
       } catch (error) {
-        throw new Error(
+        error.message =
           'An error occurred while adding the reporter at path "' +
-            path +
-            '".' +
-            error.message,
-        );
+          chalk.bold(path) +
+          '".' +
+          error.message;
+        throw error;
       }
     });
   }