feat: workerIdleMemoryLimit avoids runInBand unless explicitly set

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+- `[jest-config]` `workerIdleMemoryLimit` now defaults runInBand to false unless an explicit runInBand option is set such as `--runInBand` or `--detectOpenHandles`. Allows for linear test runs with a single worker via `--maxWorkers=1 --workerIdleMemoryLimit=500MB`. ([#13171](https://github.com/facebook/jest/pull/13171))
+
 ### Fixes
 
 ### Chore & Maintenance

docs/CLI.md

@@ -275,7 +275,7 @@ Lists all test files that Jest will run given the arguments, and exits.
 
 ### `--logHeapUsage`
 
-Logs the heap usage after every test. Useful to debug memory leaks. Use together with `--runInBand` and `--expose-gc` in node.
+Logs the heap usage after every test. Useful to debug memory leaks. Can be used together with flags like `--runInBand` or `--expose-gc` to diagnose memory leaks, etc.
 
 ### `--maxConcurrency=<num>`
 

e2e/__tests__/workerRestarting.test.ts

@@ -14,3 +14,15 @@ it('all 3 test files should complete', () => {
   const {summary} = extractSummary(result.stderr);
   expect(summary).toMatchSnapshot();
 });
+
+it.each(['runInBand', 'detectOpenHandles'])(
+  'should warn when used with %s',
+  arg => {
+    const result = runJest('worker-restarting', [`--${arg}`]);
+
+    expect(result.exitCode).toBe(0);
+    expect(result.stderr).toMatch(
+      `workerIdleMemoryLimit does not work in combination with ${arg}`,
+    );
+  },
+);

packages/jest-config/src/__tests__/getMaxWorkers.test.ts

@@ -8,8 +8,14 @@
 
 import getMaxWorkers from '../getMaxWorkers';
 
+const logWarnSpy = jest.spyOn(console, 'warn').mockReturnValue(undefined);
+
 jest.mock('os');
 
+beforeEach(() => {
+  logWarnSpy.mockClear();
+});
+
 describe('getMaxWorkers', () => {
   beforeEach(() => {
     require('os').__setCpus({length: 4});
@@ -20,6 +26,27 @@ describe('getMaxWorkers', () => {
     expect(getMaxWorkers(argv)).toBe(1);
   });
 
+  it('Returns 1 when runInBand but also logs warning if an argv memory limit is set', () => {
+    const argv = {runInBand: true, workerIdleMemoryLimit: 6000};
+    expect(getMaxWorkers(argv)).toBe(1);
+
+    expect(logWarnSpy).toHaveBeenCalledTimes(1);
+    expect(logWarnSpy).toHaveBeenCalledWith(
+      'workerIdleMemoryLimit does not work in combination with runInBand',
+    );
+  });
+
+  it('Returns 1 when runInBand but also logs warning if a config memory limit is set', () => {
+    const argv = {runInBand: true};
+    const options = {workerIdleMemoryLimit: 6000};
+    expect(getMaxWorkers(argv, options)).toBe(1);
+
+    expect(logWarnSpy).toHaveBeenCalledTimes(1);
+    expect(logWarnSpy).toHaveBeenCalledWith(
+      'workerIdleMemoryLimit does not work in combination with runInBand',
+    );
+  });
+
   it('Returns 1 when the OS CPUs are not available', () => {
     require('os').__setCpus(undefined);
     expect(getMaxWorkers({})).toBe(1);

packages/jest-config/src/getMaxWorkers.ts

@@ -10,11 +10,29 @@ import type {Config} from '@jest/types';
 
 export default function getMaxWorkers(
   argv: Partial<
-    Pick<Config.Argv, 'maxWorkers' | 'runInBand' | 'watch' | 'watchAll'>
+    Pick<
+      Config.Argv,
+      | 'maxWorkers'
+      | 'runInBand'
+      | 'watch'
+      | 'watchAll'
+      | 'workerIdleMemoryLimit'
+    >
+  >,
+  defaultOptions?: Partial<
+    Pick<Config.Argv, 'maxWorkers' | 'workerIdleMemoryLimit'>
   >,
-  defaultOptions?: Partial<Pick<Config.Argv, 'maxWorkers'>>,
 ): number {
+  const workerIdleMemoryLimit =
+    argv.workerIdleMemoryLimit ?? defaultOptions?.workerIdleMemoryLimit;
+
   if (argv.runInBand) {
+    if (workerIdleMemoryLimit) {
+      console.warn(
+        'workerIdleMemoryLimit does not work in combination with runInBand',
+      );
+    }
+
     return 1;
   } else if (argv.maxWorkers) {
     return parseWorkers(argv.maxWorkers);

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

@@ -20,27 +20,63 @@ const getTestMock = () => ({
   path: './test/path.js',
 });
 
+const logWarnSpy = jest.spyOn(console, 'warn').mockReturnValue(undefined);
+
 const getTestsMock = () => [getTestMock(), getTestMock()];
 
 test.each`
-  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}
+  tests              | timings        | detectOpenHandles | maxWorkers   | watch    | workerIdleMemoryLimit | expectedResult
+  ${[getTestMock()]} | ${[500, 500]}  | ${false}          | ${undefined} | ${true}  | ${undefined}          | ${true}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${1}         | ${true}  | ${undefined}          | ${true}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${2}         | ${true}  | ${undefined}          | ${false}
+  ${[getTestMock()]} | ${[2000, 500]} | ${false}          | ${undefined} | ${true}  | ${undefined}          | ${false}
+  ${getTestMock()}   | ${[500, 500]}  | ${false}          | ${undefined} | ${true}  | ${undefined}          | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${1}         | ${false} | ${undefined}          | ${true}
+  ${getTestMock()}   | ${[2000, 500]} | ${false}          | ${2}         | ${false} | ${undefined}          | ${false}
+  ${[getTestMock()]} | ${[2000]}      | ${false}          | ${undefined} | ${false} | ${undefined}          | ${true}
+  ${getTestsMock()}  | ${[500, 500]}  | ${false}          | ${undefined} | ${false} | ${undefined}          | ${true}
+  ${new Array(45)}   | ${[500]}       | ${false}          | ${undefined} | ${false} | ${undefined}          | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${undefined} | ${false} | ${undefined}          | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${true}           | ${undefined} | ${false} | ${undefined}          | ${true}
+  ${[getTestMock()]} | ${[500, 500]}  | ${false}          | ${undefined} | ${true}  | ${5000}               | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${1}         | ${true}  | ${5000}               | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${0}         | ${true}  | ${5000}               | ${false}
+  ${[getTestMock()]} | ${[2000]}      | ${false}          | ${undefined} | ${false} | ${5000}               | ${false}
+  ${getTestsMock()}  | ${[500, 500]}  | ${false}          | ${undefined} | ${false} | ${5000}               | ${false}
 `(
   'shouldRunInBand() - should return $expectedResult for runInBand mode',
-  ({tests, timings, detectOpenHandles, maxWorkers, watch, expectedResult}) => {
+  ({
+    tests,
+    timings,
+    detectOpenHandles,
+    maxWorkers,
+    watch,
+    workerIdleMemoryLimit,
+    expectedResult,
+  }) => {
     expect(
-      shouldRunInBand(tests, timings, {detectOpenHandles, maxWorkers, watch}),
+      shouldRunInBand(tests, timings, {
+        detectOpenHandles,
+        maxWorkers,
+        watch,
+        workerIdleMemoryLimit,
+      }),
     ).toBe(expectedResult);
   },
 );
+
+test('should log warn for incompatible flags', () => {
+  expect(
+    shouldRunInBand(getTestsMock(), [500], {
+      detectOpenHandles: true,
+      maxWorkers: 1,
+      watch: true,
+      workerIdleMemoryLimit: 5000,
+    }),
+  ).toBe(true);
+
+  expect(logWarnSpy).toHaveBeenCalledTimes(1);
+  expect(logWarnSpy).toHaveBeenCalledWith(
+    'workerIdleMemoryLimit does not work in combination with detectOpenHandles',
+  );
+});

packages/jest-core/src/testSchedulerHelper.ts

@@ -13,11 +13,25 @@ const SLOW_TEST_TIME = 1000;
 export function shouldRunInBand(
   tests: Array<Test>,
   timings: Array<number>,
-  {detectOpenHandles, maxWorkers, watch, watchAll}: Config.GlobalConfig,
+  {
+    detectOpenHandles,
+    maxWorkers,
+    watch,
+    watchAll,
+    workerIdleMemoryLimit,
+  }: Config.GlobalConfig,
 ): boolean {
   // detectOpenHandles makes no sense without runInBand, because it cannot detect leaks in workers
   if (detectOpenHandles) {
+    if (workerIdleMemoryLimit) {
+      console.warn(
+        'workerIdleMemoryLimit does not work in combination with detectOpenHandles',
+      );
+    }
+
     return true;
+  } else if (workerIdleMemoryLimit) {
+    return false;
   }
 
   /*

website/versioned_docs/version-25.x/CLI.md

@@ -248,7 +248,7 @@ Lists all test files that Jest will run given the arguments, and exits.
 
 ### `--logHeapUsage`
 
-Logs the heap usage after every test. Useful to debug memory leaks. Use together with `--runInBand` and `--expose-gc` in node.
+Logs the heap usage after every test. Useful to debug memory leaks. Can be used together with flags like `--runInBand` or `--expose-gc` to diagnose memory leaks, etc.
 
 ### `--maxConcurrency=<num>`
 

website/versioned_docs/version-26.x/CLI.md

@@ -238,7 +238,7 @@ Lists all test files that Jest will run given the arguments, and exits.
 
 ### `--logHeapUsage`
 
-Logs the heap usage after every test. Useful to debug memory leaks. Use together with `--runInBand` and `--expose-gc` in node.
+Logs the heap usage after every test. Useful to debug memory leaks. Can be used together with flags like `--runInBand` or `--expose-gc` to diagnose memory leaks, etc.
 
 ### `--maxConcurrency=<num>`
 

website/versioned_docs/version-27.x/CLI.md

@@ -234,7 +234,7 @@ Lists all test files that Jest will run given the arguments, and exits.
 
 ### `--logHeapUsage`
 
-Logs the heap usage after every test. Useful to debug memory leaks. Use together with `--runInBand` and `--expose-gc` in node.
+Logs the heap usage after every test. Useful to debug memory leaks. Can be used together with flags like `--runInBand` or `--expose-gc` to diagnose memory leaks, etc.
 
 ### `--maxConcurrency=<num>`
 

website/versioned_docs/version-28.x/CLI.md

@@ -275,7 +275,7 @@ Lists all test files that Jest will run given the arguments, and exits.
 
 ### `--logHeapUsage`
 
-Logs the heap usage after every test. Useful to debug memory leaks. Use together with `--runInBand` and `--expose-gc` in node.
+Logs the heap usage after every test. Useful to debug memory leaks. Can be used together with flags like `--runInBand` or `--expose-gc` to diagnose memory leaks, etc.
 
 ### `--maxConcurrency=<num>`
 

website/versioned_docs/version-29.0/CLI.md

@@ -275,7 +275,7 @@ Lists all test files that Jest will run given the arguments, and exits.
 
 ### `--logHeapUsage`
 
-Logs the heap usage after every test. Useful to debug memory leaks. Use together with `--runInBand` and `--expose-gc` in node.
+Logs the heap usage after every test. Useful to debug memory leaks. Can be used together with flags like `--runInBand` or `--expose-gc` to diagnose memory leaks, etc.
 
 ### `--maxConcurrency=<num>`