--logHeapUsage: also log process id

This is meant to aid dealing with #11956

--logHeapUsage after each test logs the heap size of whatever worker
happened to run it, but because results are interleaved from multiple
workers, one has to guess which heap sizes came from different workers
(jest doesn't even log how many workers are involved).

=> This adds the process id:

    PASS src/BlaBla.test.ts (9.64 s, pid 1085066: 266 MB heap size)

Making it easy to focus on a single worker's heap history,
or plot each worker's progression separately:

    egrep --only-matching 'pid.*heap size' JEST_OUTPUT.txt |
      sort --field-separator=' ' --key=2 --numeric --stable

Printing OS process ids also allows correlating with other perf tools like `top`.
It also reflects workers getting shutdown/replaced with `--workerIdleMemoryLimit`:

    PASS __tests__/test1.js (pid 1104509: 22 MB heap size)
    PASS __tests__/test2.js (pid 1104519: 22 MB heap size)
    PASS __tests__/test3.js (pid 1104529: 22 MB heap size)

e2e/Utils.ts

@@ -310,6 +310,15 @@ export const extractSummaries = (
     .map(({start, end}) => extractSortedSummary(stdout.slice(start, end)));
 };
 
+/** Only works in --logHeapUsage mode. */
+export const extractWorkerPids = (stdout: string) => {
+  const processIds = new Set<string>();
+  for (const groups of stdout.matchAll(/(?:PASS|FAIL) .*pid (\d+)/gm)) {
+    processIds.add(groups[1]);
+  }
+  return processIds;
+};
+
 // Certain environments (like CITGM and GH Actions) do not come with mercurial installed
 let hgIsInstalled: boolean | null = null;
 

e2e/__tests__/logHeapUsage.test.ts

@@ -22,5 +22,7 @@ test('logs memory usage', () => {
   });
 
   const {stderr} = runJest(DIR, ['--logHeapUsage']);
-  expect(stderr).toMatch(/PASS\s__tests__\/a-banana.js.*\d+ MB heap size/);
+  expect(stderr).toMatch(
+    /PASS\s__tests__\/a-banana.js.*pid \d+: \d+ MB heap size/,
+  );
 });

e2e/__tests__/workerRestarting.test.ts

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {extractSummary} from '../Utils';
+import {extractSummary, extractWorkerPids} from '../Utils';
 import runJest from '../runJest';
 
 it('all 3 test files should complete', () => {
@@ -14,3 +14,17 @@ it('all 3 test files should complete', () => {
   const {summary} = extractSummary(result.stderr);
   expect(summary).toMatchSnapshot();
 });
+
+it('3 different worker processes should get used', () => {
+  const result = runJest('worker-restarting', ['--logHeapUsage']);
+  const processIds = extractWorkerPids(result.stderr);
+  expect([...processIds]).toHaveLength(3);
+});
+
+it('2 worker processes should be kept with high limit', () => {
+  // This could get flaky if memory usage on tiny test becomes much worse,
+  // but that'd be good to notice ;-).  As of this writing, I've seen 20-43 MB.
+  const result = runJest('worker-not-restarting', ['--logHeapUsage']);
+  const processIds = extractWorkerPids(result.stderr);
+  expect([...processIds]).toHaveLength(2);
+});

e2e/worker-not-restarting/__tests__/test1.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('basic test', () => {
+  expect(true).toBeTruthy();
+});

e2e/worker-not-restarting/__tests__/test2.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('basic test', () => {
+  expect(true).toBeTruthy();
+});

e2e/worker-not-restarting/__tests__/test3.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('basic test', () => {
+  expect(true).toBeTruthy();
+});

e2e/worker-not-restarting/package.json

@@ -0,0 +1,6 @@
+{
+  "jest": {
+    "maxWorkers": 2,
+    "workerIdleMemoryLimit": "200MB"
+  }
+}

packages/jest-reporters/src/getResultHeader.ts

@@ -45,7 +45,9 @@ export default function getResultHeader(
 
   if (result.memoryUsage) {
     const toMB = (bytes: number) => Math.floor(bytes / 1024 / 1024);
-    testDetail.push(`${toMB(result.memoryUsage)} MB heap size`);
+    testDetail.push(
+      `pid ${result.workerProcessId}: ${toMB(result.memoryUsage)} MB heap size`
+    );
   }
 
   const projectDisplayName =

packages/jest-runner/src/runTest.ts

@@ -336,6 +336,7 @@ async function runTestInternal(
     result.console = testConsole.getBuffer();
     result.skipped = testCount === result.numPendingTests;
     result.displayName = projectConfig.displayName;
+    result.workerProcessId = process.pid;
 
     const coverage = runtime.getAllCoverageInfoCopy();
     if (coverage) {

packages/jest-test-result/src/types.ts

@@ -94,6 +94,7 @@ export type TestResult = {
   failureMessage?: string | null;
   leaks: boolean;
   memoryUsage?: number;
+  workerProcessId?: number;
   numFailingTests: number;
   numPassingTests: number;
   numPendingTests: number;