test_runner: emit test:watch-drained event

Author: MoLow

doc/api/test.md

@@ -1539,6 +1539,10 @@ This event is only emitted if `--test` flag is passed.
 Emitted when a running test writes to `stdout`.
 This event is only emitted if `--test` flag is passed.
 
+### Event: `'test:watch-drained'`
+
+Emitted when no more tests are queued for execution in watch mode.
+
 ## Class: `TestContext`
 
 <!-- YAML

lib/internal/test_runner/runner.js

@@ -335,9 +335,6 @@ class FileTest extends Test {
   }
 }
 
-const runningProcesses = new SafeMap();
-const runningSubtests = new SafeMap();
-
 function runTestFile(path, root, inspectPort, filesWatcher, testNamePatterns) {
   const subtest = root.createSubtest(FileTest, path, async (t) => {
     const args = getRunArgs({ path, inspectPort, testNamePatterns });
@@ -352,11 +349,11 @@ function runTestFile(path, root, inspectPort, filesWatcher, testNamePatterns) {
     }
 
     const child = spawn(process.execPath, args, { signal: t.signal, encoding: 'utf8', env, stdio });
-    runningProcesses.set(path, child);
+    filesWatcher?.runningProcesses.set(path, child);
+    filesWatcher?.watcher.watchChildProcessModules(child, path);
 
     let err;
 
-    filesWatcher?.watchChildProcessModules(child, path);
 
     child.on('error', (error) => {
       err = error;
@@ -388,8 +385,12 @@ function runTestFile(path, root, inspectPort, filesWatcher, testNamePatterns) {
       finished(child.stdout, { signal: t.signal }),
     ]);
 
-    runningProcesses.delete(path);
-    runningSubtests.delete(path);
+    filesWatcher?.runningProcesses.delete(path);
+    filesWatcher?.runningSubtests.delete(path);
+    if (filesWatcher?.runningSubtests.size === 0) {
+      root.reporter[kEmitMessage]('test:watch-drained');
+    }
+
     if (code !== 0 || signal !== null) {
       if (!err) {
         const failureType = subtest.failedSubtests ? kSubtestsFailed : kTestCodeFailure;
@@ -410,9 +411,13 @@ function runTestFile(path, root, inspectPort, filesWatcher, testNamePatterns) {
 }
 
 function watchFiles(testFiles, root, inspectPort, signal, testNamePatterns) {
-  const filesWatcher = new FilesWatcher({ throttle: 500, mode: 'filter' });
-  filesWatcher.on('changed', ({ owners }) => {
-    filesWatcher.unfilterFilesOwnedBy(owners);
+  const runningProcesses = new SafeMap();
+  const runningSubtests = new SafeMap();
+  const watcher = new FilesWatcher({ throttle: 500, mode: 'filter' });
+  const filesWatcher = { __proto__: null, watcher, runningProcesses, runningSubtests };
+
+  watcher.on('changed', ({ owners }) => {
+    watcher.unfilterFilesOwnedBy(owners);
     PromisePrototypeThen(SafePromiseAllReturnVoid(testFiles, async (file) => {
       if (!owners.has(file)) {
         return;
@@ -433,9 +438,10 @@ function watchFiles(testFiles, root, inspectPort, signal, testNamePatterns) {
     }));
   });
   signal?.addEventListener('abort', () => {
-    filesWatcher.clear();
+    watcher.clear();
     root.postRun();
   }, { __proto__: null, once: true });
+
   return filesWatcher;
 }
 
@@ -485,7 +491,7 @@ function run(options) {
     root.harness.bootstrapComplete = true;
     return SafePromiseAllSettledReturnVoid(testFiles, (path) => {
       const subtest = runTestFile(path, root, inspectPort, filesWatcher, testNamePatterns);
-      runningSubtests.set(path, subtest);
+      filesWatcher?.runningSubtests.set(path, subtest);
       return subtest;
     });
   };

test/parallel/test-runner-run.mjs

@@ -132,4 +132,15 @@ describe('require(\'node:test\').run', { concurrency: true }, () => {
       .toArray();
     assert.deepStrictEqual(result, ['this should pass']);
   });
+
+  it('should emit "test:watch-drained" event on watch mode', async () => {
+    const controller = new AbortController();
+    await run({ files: [join(testFixtures, 'test/random.cjs')], watch: true, signal: controller.signal })
+      .on('data', function({ type }) {
+        console.log(type);
+        if (type === 'test:watch-drained') {
+          controller.abort();
+        }
+      });
+  });
 });