test_runner: fix watch mode race condition

PR-URL: #52954
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>

lib/internal/test_runner/runner.js

@@ -35,7 +35,6 @@ const { createInterface } = require('readline');
 const { deserializeError } = require('internal/error_serdes');
 const { Buffer } = require('buffer');
 const { FilesWatcher } = require('internal/watch_mode/files_watcher');
-const { queueMicrotask } = require('internal/process/task_queues');
 const console = require('internal/console/global');
 const {
   codes: {
@@ -420,10 +419,16 @@ function runTestFile(path, filesWatcher, opts) {
     if (watchMode) {
       filesWatcher.runningProcesses.delete(path);
       filesWatcher.runningSubtests.delete(path);
-      if (filesWatcher.runningSubtests.size === 0) {
-        opts.root.reporter[kEmitMessage]('test:watch:drained');
-        queueMicrotask(() => opts.root.postRun());
-      }
+      (async () => {
+        try {
+          await subTestEnded;
+        } finally {
+          if (filesWatcher.runningSubtests.size === 0) {
+            opts.root.reporter[kEmitMessage]('test:watch:drained');
+            opts.root.postRun();
+          }
+        }
+      })();
     }
 
     if (code !== 0 || signal !== null) {
@@ -442,7 +447,8 @@ function runTestFile(path, filesWatcher, opts) {
       throw err;
     }
   });
-  return subtest.start();
+  const subTestEnded = subtest.start();
+  return subTestEnded;
 }
 
 function watchFiles(testFiles, opts) {

test/parallel/test-runner-watch-mode.mjs

@@ -1,6 +1,7 @@
 // Flags: --expose-internals
 import * as common from '../common/index.mjs';
 import { describe, it } from 'node:test';
+import assert from 'node:assert';
 import { spawn } from 'node:child_process';
 import { writeFileSync } from 'node:fs';
 import util from 'internal/util';
@@ -36,21 +37,33 @@ async function testWatch({ fileToUpdate, file }) {
                       ['--watch', '--test', file ? fixturePaths[file] : undefined].filter(Boolean),
                       { encoding: 'utf8', stdio: 'pipe', cwd: tmpdir.path });
   let stdout = '';
+  let currentRun = '';
+  const runs = [];
 
   child.stdout.on('data', (data) => {
     stdout += data.toString();
-    const testRuns = stdout.match(/ - test has ran/g);
+    currentRun += data.toString();
+    const testRuns = stdout.match(/# duration_ms\s\d+/g);
     if (testRuns?.length >= 1) ran1.resolve();
     if (testRuns?.length >= 2) ran2.resolve();
   });
 
   await ran1.promise;
+  runs.push(currentRun);
+  currentRun = '';
   const content = fixtureContent[fileToUpdate];
   const path = fixturePaths[fileToUpdate];
   const interval = setInterval(() => writeFileSync(path, content), common.platformTimeout(1000));
   await ran2.promise;
+  runs.push(currentRun);
   clearInterval(interval);
   child.kill();
+  for (const run of runs) {
+    assert.match(run, /# tests 1/);
+    assert.match(run, /# pass 1/);
+    assert.match(run, /# fail 0/);
+    assert.match(run, /# cancelled 0/);
+  }
 }
 
 describe('test runner watch mode', () => {