feat: Allow transforming jest-runner

e2e/__tests__/transform.test.ts

@@ -185,3 +185,14 @@ describe('transformer-config', () => {
     expect(stdout).toMatchSnapshot();
   });
 });
+
+describe('transform-runner', () => {
+  const dir = path.resolve(__dirname, '../transform/transform-runner');
+
+  it('should transform runner', () => {
+    const {json, stderr} = runWithJson(dir, ['--no-cache']);
+    expect(stderr).toMatch(/PASS/);
+    expect(json.success).toBe(true);
+    expect(json.numPassedTests).toBe(1);
+  });
+});

e2e/transform/transform-runner/__tests__/add.test.js

@@ -0,0 +1,10 @@
+/**
+ * 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.
+ */
+
+it('should add two numbers', () => {
+  expect(1 + 1).toBe(2);
+});

e2e/transform/transform-runner/babel.config.js

@@ -0,0 +1,18 @@
+/**
+ * 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.
+ */
+
+module.exports = {
+  presets: [
+    ['@babel/preset-typescript'],
+    [
+      '@babel/preset-env',
+      {
+        targets: {node: 6},
+      },
+    ],
+  ],
+};

e2e/transform/transform-runner/package.json

@@ -0,0 +1,11 @@
+{
+  "jest": {
+    "rootDir": "./",
+    "runner": "<rootDir>/runner.ts"
+  },
+  "dependencies": {
+    "@babel/preset-env": "^7.0.0",
+    "@babel/preset-typescript": "^7.0.0",
+    "jest-environment-node": "^24.9.0"
+  }
+}

e2e/transform/transform-runner/runner.ts

@@ -0,0 +1,79 @@
+/**
+ * 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 {Config} from '@jest/types';
+import {
+  OnTestFailure,
+  OnTestStart,
+  OnTestSuccess,
+  Test,
+  TestRunnerContext,
+  TestWatcher,
+} from 'jest-runner';
+import throat from 'throat';
+import {TestResult} from '@jest/test-result';
+
+export default class BaseTestRunner {
+  private _globalConfig: Config.GlobalConfig;
+  private _context: TestRunnerContext;
+
+  constructor(globalConfig: Config.GlobalConfig, context?: TestRunnerContext) {
+    this._globalConfig = globalConfig;
+    this._context = context || {};
+  }
+
+  async runTests(
+    tests: Array<Test>,
+    watcher: TestWatcher,
+    onStart: OnTestStart,
+    onResult: OnTestSuccess,
+    onFailure: OnTestFailure
+  ): Promise<void> {
+    const mutex = throat(1);
+    return tests.reduce(
+      (promise, test) =>
+        mutex(() =>
+          promise
+            .then(async () => {
+              await onStart(test);
+              return {
+                numFailingTests: 0,
+                numPassingTests: 1,
+                numPendingTests: 0,
+                numTodoTests: 0,
+                perfStats: {
+                  end: 0,
+                  start: 0,
+                },
+                snapshot: {
+                  added: 0,
+                  fileDeleted: false,
+                  matched: 0,
+                  unchecked: 0,
+                  unmatched: 0,
+                  updated: 0,
+                },
+                testFilePath: test.path,
+                testResults: [
+                  {
+                    ancestorTitles: [],
+                    duration: 2,
+                    failureMessages: [],
+                    fullName: 'sample test',
+                    status: 'passed',
+                    title: 'sample test',
+                  },
+                ],
+              } as TestResult;
+            })
+            .then(result => onResult(test, result))
+            .catch(err => onFailure(test, err))
+        ),
+      Promise.resolve()
+    );
+  }
+}

e2e/transform/transform-runner/tsconfig.json

@@ -0,0 +1,6 @@
+{
+  "compilerOptions": {
+    "esModuleInterop": true,
+    "module": "commonjs",
+  }
+}

packages/jest-core/src/TestScheduler.ts

@@ -8,6 +8,7 @@
 import chalk from 'chalk';
 import {formatExecError} from 'jest-message-util';
 import {Config} from '@jest/types';
+import {ScriptTransformer} from '@jest/transform';
 import snapshot from 'jest-snapshot';
 import TestRunner, {Test} from 'jest-runner';
 import {Context} from 'jest-runtime';
@@ -28,6 +29,7 @@ import {
   buildFailureTestResult,
   makeEmptyAggregatedTestResult,
 } from '@jest/test-result';
+import interopRequireDefault from 'jest-util/build/interopRequireDefault';
 import ReporterDispatcher from './ReporterDispatcher';
 import TestWatcher from './TestWatcher';
 import {shouldRunInBand} from './testSchedulerHelper';
@@ -171,7 +173,10 @@ export default class TestScheduler {
     const testRunners = Object.create(null);
     contexts.forEach(({config}) => {
       if (!testRunners[config.runner]) {
-        const Runner: typeof TestRunner = require(config.runner);
+        const transformer = new ScriptTransformer(config);
+        const Runner: typeof TestRunner = interopRequireDefault(
+          transformer.requireAndTranspileModule(config.runner),
+        ).default;
         testRunners[config.runner] = new Runner(this._globalConfig, {
           changedFiles: this._context && this._context.changedFiles,
         });

packages/jest-core/src/__tests__/TestScheduler.test.js

@@ -88,6 +88,7 @@ test('schedule tests run in parallel per default', async () => {
     context: {
       config: {
         runner: 'jest-runner-parallel',
+        transform: [],
       },
       hasteFS: {
         matchFiles: jest.fn(() => []),
@@ -109,6 +110,7 @@ test('schedule tests run in serial if the runner flags them', async () => {
     context: {
       config: {
         runner: 'jest-runner-serial',
+        transform: [],
       },
       hasteFS: {
         matchFiles: jest.fn(() => []),
@@ -131,6 +133,7 @@ test('should bail after `n` failures', async () => {
       config: {
         rootDir: './',
         runner: 'jest-runner-serial',
+        transform: [],
       },
       hasteFS: {
         matchFiles: jest.fn(() => []),
@@ -161,6 +164,7 @@ test('should not bail if less than `n` failures', async () => {
       config: {
         rootDir: './',
         runner: 'jest-runner-serial',
+        transform: [],
       },
       hasteFS: {
         matchFiles: jest.fn(() => []),
@@ -190,6 +194,7 @@ test('should set runInBand to run in serial', async () => {
     context: {
       config: {
         runner: 'jest-runner-parallel',
+        transform: [],
       },
       hasteFS: {
         matchFiles: jest.fn(() => []),
@@ -214,6 +219,7 @@ test('should set runInBand to not run in serial', async () => {
     context: {
       config: {
         runner: 'jest-runner-parallel',
+        transform: [],
       },
       hasteFS: {
         matchFiles: jest.fn(() => []),