detectOpenHandles imply runInBand (#8283)

* pass config into shouldRunInBand

* detectOpenHandles imply runInBand

* Update CHANGELOG.md

* docs

Author: jeysal

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixes
 
 - `[jest-snapshot]` Inline snapshots: do not indent empty lines ([#8277](https://github.com/facebook/jest/pull/8277))
+- `[jest-core]` Make `detectOpenHandles` imply `runInBand` ([#8283](https://github.com/facebook/jest/pull/8283))
 
 ### Chore & Maintenance
 

docs/CLI.md

@@ -158,7 +158,7 @@ Print debugging info about your Jest config.
 
 ### `--detectOpenHandles`
 
-Attempt to collect and print open handles preventing Jest from exiting cleanly. Use this in cases where you need to use `--forceExit` in order for Jest to exit to potentially track down the reason. Implemented using [`async_hooks`](https://nodejs.org/api/async_hooks.html), so it only works in Node 8 and newer.
+Attempt to collect and print open handles preventing Jest from exiting cleanly. Use this in cases where you need to use `--forceExit` in order for Jest to exit to potentially track down the reason. This implies `--runInBand`, making tests run serially. Implemented using [`async_hooks`](https://nodejs.org/api/async_hooks.html), so it only works in Node 8 and newer. This option has a significant performance penalty and should only be used for debugging.
 
 ### `--env=<environment>`
 

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

@@ -229,7 +229,7 @@ export const options = {
     default: false,
     description:
       'Print out remaining open handles preventing Jest from exiting at the ' +
-      'end of a test run.',
+      'end of a test run. Implies `runInBand`.',
     type: 'boolean' as 'boolean',
   },
   env: {

packages/jest-core/src/TestScheduler.ts

@@ -86,12 +86,7 @@ export default class TestScheduler {
       getEstimatedTime(timings, this._globalConfig.maxWorkers) / 1000,
     );
 
-    const runInBand = shouldRunInBand(
-      tests,
-      this._globalConfig.watch || this._globalConfig.watchAll,
-      this._globalConfig.maxWorkers,
-      timings,
-    );
+    const runInBand = shouldRunInBand(tests, timings, this._globalConfig);
 
     const onResult = async (test: Test, testResult: TestResult) => {
       if (watcher.isInterrupted()) {

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

@@ -23,23 +23,24 @@ const getTestMock = () => ({
 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}
+  tests              | timings        | detectOpenHandles | maxWorkers   | watch    | expectedResult
+  ${[getTestMock()]} | ${[500, 500]}  | ${false}          | ${undefined} | ${true}  | ${true}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${1}         | ${true}  | ${true}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${2}         | ${true}  | ${false}
+  ${[getTestMock()]} | ${[2000, 500]} | ${false}          | ${undefined} | ${true}  | ${false}
+  ${getTestMock()}   | ${[500, 500]}  | ${false}          | ${undefined} | ${true}  | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${1}         | ${false} | ${true}
+  ${getTestMock()}   | ${[2000, 500]} | ${false}          | ${2}         | ${false} | ${false}
+  ${[getTestMock()]} | ${[2000]}      | ${false}          | ${undefined} | ${false} | ${true}
+  ${getTestsMock()}  | ${[500, 500]}  | ${false}          | ${undefined} | ${false} | ${true}
+  ${new Array(45)}   | ${[500]}       | ${false}          | ${undefined} | ${false} | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${undefined} | ${false} | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${true}           | ${undefined} | ${false} | ${true}
 `(
   'shouldRunInBand() - should return $expectedResult for runInBand mode',
-  ({tests, watch, maxWorkers, timings, expectedResult}) => {
-    expect(shouldRunInBand(tests, watch, maxWorkers, timings)).toBe(
-      expectedResult,
-    );
+  ({tests, timings, detectOpenHandles, maxWorkers, watch, expectedResult}) => {
+    expect(
+      shouldRunInBand(tests, timings, {detectOpenHandles, maxWorkers, watch}),
+    ).toBe(expectedResult);
   },
 );

packages/jest-core/src/testSchedulerHelper.ts

@@ -5,17 +5,22 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import {Config} from '@jest/types';
 import {Test} from 'jest-runner';
 
 const SLOW_TEST_TIME = 1000;
 
 export function shouldRunInBand(
   tests: Array<Test>,
-  isWatchMode: boolean,
-  maxWorkers: number,
   timings: Array<number>,
+  {detectOpenHandles, maxWorkers, watch, watchAll}: Config.GlobalConfig,
 ) {
-  /**
+  // detectOpenHandles makes no sense without runInBand, because it cannot detect leaks in workers
+  if (detectOpenHandles) {
+    return true;
+  }
+
+  /*
    * 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
@@ -26,6 +31,7 @@ export function shouldRunInBand(
    * force running in band.
    * https://github.com/facebook/jest/blob/700e0dadb85f5dc8ff5dac6c7e98956690049734/packages/jest-config/src/getMaxWorkers.js#L14-L17
    */
+  const isWatchMode = watch || watchAll;
   const areFastTests = timings.every(timing => timing < SLOW_TEST_TIME);
   const oneWorkerOrLess = maxWorkers <= 1;
   const oneTestOrLess = tests.length <= 1;