feat: allow to use workerIdleMemoryLimit with only 1 worker or runInBand option

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[jest-core]` allow to use workerIdleMemoryLimit with only 1 worker or runInBand option ([#13846](https://github.com/facebook/jest/pull/13846))
 - `[jest-message-util]` Add support for [error causes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause) ([#13868](https://github.com/facebook/jest/pull/13868) & [#13912](https://github.com/facebook/jest/pull/13912))
 
 ### Fixes

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

@@ -23,24 +23,43 @@ const getTestMock = () => ({
 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}  | ${'500MB'}            | ${true}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${1}         | ${true}  | ${'500MB'}            | ${true}
+  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${1}         | ${false} | ${'500MB'}            | ${false}
+  ${[getTestMock()]} | ${[2000]}      | ${false}          | ${undefined} | ${false} | ${'500MB'}            | ${false}
+  ${getTestsMock()}  | ${[500, 500]}  | ${false}          | ${undefined} | ${false} | ${'500MB'}            | ${false}
+  ${getTestsMock()}  | ${[2000, 500]} | ${true}           | ${undefined} | ${false} | ${'500MB'}            | ${true}
 `(
   '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);
   },
 );

packages/jest-core/src/testSchedulerHelper.ts

@@ -13,7 +13,13 @@ 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) {
@@ -41,8 +47,10 @@ export function shouldRunInBand(
   }
 
   return (
-    oneWorkerOrLess ||
-    oneTestOrLess ||
-    (tests.length <= 20 && timings.length > 0 && areFastTests)
+    // When specifying a memory limit, workers should be used
+    !workerIdleMemoryLimit &&
+    (oneWorkerOrLess ||
+      oneTestOrLess ||
+      (tests.length <= 20 && timings.length > 0 && areFastTests))
   );
 }