fix: TestScheduler now take in count the runInBand config

CHANGELOG.md

@@ -82,6 +82,7 @@
 - `[jest-haste-map]` Fix `require` detection with trailing commas and ignore `import typeof` modules ([#7385](https://github.com/facebook/jest/pull/7385))
 - `[jest-cli]` Fix to set prettierPath via config file ([#7412](https://github.com/facebook/jest/pull/7412))
 - `[jest-cli]` Support dashed args ([#7497](https://github.com/facebook/jest/pull/7497))
+- `[jest-cli]` Fix to run in band tests if watch mode enable when runInBand arg used ([#7518](https://github.com/facebook/jest/pull/7518))
 
 ### Chore & Maintenance
 

e2e/__tests__/failures.test.js

@@ -43,7 +43,7 @@ test('works with node assert', () => {
 
   // Node 9 started to include the error for `doesNotThrow`
   // https://github.com/nodejs/node/pull/12167
-  if (nodeMajorVersion >= 8) {
+  if (nodeMajorVersion >= 9) {
     expect(summary).toContain(`
     assert.doesNotThrow(function)
 
@@ -71,7 +71,7 @@ test('works with node assert', () => {
       Got unwanted exception.
 `;
 
-    if (nodeMajorVersion === 8 || nodeMajorVersion === 9) {
+    if (nodeMajorVersion === 9) {
       const specificErrorMessage = `Message:
       Got unwanted exception.
     err!

packages/jest-cli/src/TestScheduler.js

@@ -29,8 +29,7 @@ import SummaryReporter from './reporters/summary_reporter';
 import TestRunner from 'jest-runner';
 import TestWatcher from './TestWatcher';
 import VerboseReporter from './reporters/verbose_reporter';
-
-const SLOW_TEST_TIME = 1000;
+import {shouldRunInBand} from './testSchedulerHelper';
 
 // The default jest-runner is required because it is the default test runner
 // and required implicitly through the `runner` ProjectConfig option.
@@ -85,25 +84,12 @@ export default class TestScheduler {
       getEstimatedTime(timings, this._globalConfig.maxWorkers) / 1000,
     );
 
-    // Run in band if we only have one test or one worker available, unless we
-    // are using the watch mode, in which case the TTY has to be responsive and
-    // we cannot schedule anything in the main thread. Same logic applies to
-    // watchAll.
-    //
-    // If we are confident from previous runs that the tests will finish
-    // quickly we also run in band to reduce the overhead of spawning workers.
-    const areFastTests = timings.every(timing => timing < SLOW_TEST_TIME);
-
-    const runInBandWatch = tests.length <= 1 && areFastTests;
-    const runInBandNonWatch =
-      this._globalConfig.maxWorkers <= 1 ||
-      tests.length <= 1 ||
-      (tests.length <= 20 && timings.length > 0 && areFastTests);
-
-    const runInBand =
-      this._globalConfig.watch || this._globalConfig.watchAll
-        ? runInBandWatch
-        : runInBandNonWatch;
+    const runInBand = shouldRunInBand(
+      tests,
+      this._globalConfig.watch || this._globalConfig.watchAll,
+      this._globalConfig.maxWorkers,
+      timings,
+    );
 
     const onResult = async (test: Test, testResult: TestResult) => {
       if (watcher.isInterrupted()) {

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

@@ -10,6 +10,7 @@
 
 import TestScheduler from '../TestScheduler';
 import SummaryReporter from '../reporters/summary_reporter';
+import * as testSchedulerHelper from '../testSchedulerHelper';
 
 jest.mock('../reporters/default_reporter');
 const mockSerialRunner = {
@@ -27,8 +28,12 @@ jest.mock('jest-runner-parallel', () => jest.fn(() => mockParallelRunner), {
   virtual: true,
 });
 
+const spyShouldRunInBand = jest.spyOn(testSchedulerHelper, 'shouldRunInBand');
+
 beforeEach(() => {
   mockSerialRunner.runTests.mockClear();
+  mockParallelRunner.runTests.mockClear();
+  spyShouldRunInBand.mockClear();
 });
 
 test('config for reporters supports `default`', () => {
@@ -180,3 +185,51 @@ test('should not bail if less than `n` failures', async () => {
   });
   expect(setState).not.toBeCalled();
 });
+
+test('should set runInBand to run in serial', async () => {
+  const scheduler = new TestScheduler({}, {});
+  const test = {
+    context: {
+      config: {
+        runner: 'jest-runner-parallel',
+      },
+      hasteFS: {
+        matchFiles: jest.fn(() => []),
+      },
+    },
+    path: './test/path.js',
+  };
+  const tests = [test, test];
+
+  spyShouldRunInBand.mockReturnValue(true);
+
+  await scheduler.scheduleTests(tests, {isInterrupted: jest.fn()});
+
+  expect(spyShouldRunInBand).toHaveBeenCalled();
+  expect(mockParallelRunner.runTests).toHaveBeenCalled();
+  expect(mockParallelRunner.runTests.mock.calls[0][5].serial).toBeTruthy();
+});
+
+test('should set runInBand to not run in serial', async () => {
+  const scheduler = new TestScheduler({}, {});
+  const test = {
+    context: {
+      config: {
+        runner: 'jest-runner-parallel',
+      },
+      hasteFS: {
+        matchFiles: jest.fn(() => []),
+      },
+    },
+    path: './test/path.js',
+  };
+  const tests = [test, test];
+
+  spyShouldRunInBand.mockReturnValue(false);
+
+  await scheduler.scheduleTests(tests, {isInterrupted: jest.fn()});
+
+  expect(spyShouldRunInBand).toHaveBeenCalled();
+  expect(mockParallelRunner.runTests).toHaveBeenCalled();
+  expect(mockParallelRunner.runTests.mock.calls[0][5].serial).toBeFalsy();
+});

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

@@ -0,0 +1,45 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ */
+'use strict';
+
+import {shouldRunInBand} from '../testSchedulerHelper';
+
+const getTestMock = () => ({
+  context: {
+    config: {
+      runner: 'jest-runner-parallel',
+    },
+    hasteFS: {
+      matchFiles: jest.fn(() => []),
+    },
+  },
+  path: './test/path.js',
+});
+
+const getTestsMock = () => [getTestMock(), getTestMock()];
+
+test.each`
+  tests              | watch    | maxWorkers   | timings        | expectedResult
+  ${[getTestMock()]} | ${true}  | ${undefined} | ${[500, 500]}  | ${true}
+  ${getTestsMock()}  | ${true}  | ${1}         | ${[2000, 500]} | ${true}
+  ${getTestsMock()}  | ${true}  | ${2}         | ${[2000, 500]} | ${false}
+  ${[getTestMock()]} | ${true}  | ${undefined} | ${[2000, 500]} | ${false}
+  ${getTestMock()}   | ${true}  | ${undefined} | ${[500, 500]}  | ${false}
+  ${getTestsMock()}  | ${false} | ${1}         | ${[2000, 500]} | ${true}
+  ${getTestMock()}   | ${false} | ${2}         | ${[2000, 500]} | ${false}
+  ${[getTestMock()]} | ${false} | ${undefined} | ${[2000]}      | ${true}
+  ${getTestsMock()}  | ${false} | ${undefined} | ${[500, 500]}  | ${true}
+  ${new Array(45)}   | ${false} | ${undefined} | ${[500]}       | ${false}
+  ${getTestsMock()}  | ${false} | ${undefined} | ${[2000, 500]} | ${false}
+`(
+  'shouldRunInBand() - should return $expectedResult for runInBand mode',
+  ({tests, watch, maxWorkers, timings, expectedResult}) => {
+    expect(shouldRunInBand(tests, watch, maxWorkers, timings)).toBe(
+      expectedResult,
+    );
+  },
+);

packages/jest-cli/src/testSchedulerHelper.js

@@ -0,0 +1,42 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ *
+ * @flow
+ */
+'use strict';
+import type {Test} from 'types/TestRunner';
+
+const SLOW_TEST_TIME = 1000;
+
+export function shouldRunInBand(
+  tests: Array<Test>,
+  isWatchMode: boolean,
+  maxWorkers: number,
+  timings: number[],
+) {
+  // Run in band if we only have one test or one worker available, unless we
+  // are using the watch mode, in which case the TTY has to be responsive and
+  // we cannot schedule anything in the main thread. Same logic applies to
+  // watchAll.
+  //
+  // If we are confident from previous runs that the tests will finish
+  // quickly we also run in band to reduce the overhead of spawning workers.
+  const areFastTests = timings.every(timing => timing < SLOW_TEST_TIME);
+  // This apply also when runInBand arg present
+  // https://github.com/facebook/jest/blob/700e0dadb85f5dc8ff5dac6c7e98956690049734/packages/jest-config/src/getMaxWorkers.js#L14-L17
+  const oneWorkerOrLess = maxWorkers <= 1;
+  const oneTestOrLess = tests.length <= 1;
+
+  if (isWatchMode) {
+    return oneWorkerOrLess || (oneTestOrLess && areFastTests);
+  }
+
+  return (
+    oneWorkerOrLess ||
+    oneTestOrLess ||
+    (tests.length <= 20 && timings.length > 0 && areFastTests)
+  );
+}