test: fix flaky test-watch-mode-kill-signal-*

After the write triggers a restart of the grandchild, the newly
spawned second grandchild can post another 'script ready' message
before the stdout from the first grandchild is relayed by the
watcher and processed by this parent process to kill
the watcher. If we write again and trigger another restart, we can
end up in an infinite loop and never receive the stdout of the
grandchildren in time.
Only write once to verify the first grandchild process receives
the expected signal. We don't care about the subsequent grandchild
processes.

Author: joyeecheung

test/parallel/test-watch-mode-kill-signal-default.mjs

@@ -27,15 +27,28 @@ const child = spawn(
 
 let stdout = '';
 child.stdout.on('data', (data) => {
-  stdout += `${data}`;
+  let dataStr = data.toString();
+  console.log(`[STDOUT] ${dataStr}`);
+  stdout += `${dataStr}`;
   if (/__(SIGINT|SIGTERM) received__/.test(stdout)) {
+    console.log(`[PARENT] Sending kill signal to child process: ${child.pid}`);
     child.kill();
   }
 });
 
+// After the write triggers a restart of the grandchild, the newly spawned second
+// grandchild can post another 'script ready' message before the stdout from the first
+// grandchild is relayed by the watcher and processed by this parent process to kill
+// the watcher. If we write again and trigger another restart, we can
+// end up in an infinite loop and never receive the stdout of the grandchildren in time.
+// Only write once to verify the first grandchild process receives the expected signal.
+// We don't care about the subsequent grandchild processes.
+let written = false;
 child.on('message', (msg) => {
-  if (msg === 'script ready') {
+  console.log(`[MESSAGE]`, msg);
+  if (msg === 'script ready' && !written) {
     writeFileSync(indexPath, indexContents);
+    written = true;
   }
 });
 

test/parallel/test-watch-mode-kill-signal-override.mjs

@@ -28,15 +28,28 @@ const child = spawn(
 
 let stdout = '';
 child.stdout.on('data', (data) => {
-  stdout += `${data}`;
+  let dataStr = data.toString();
+  console.log(`[STDOUT] ${dataStr}`);
+  stdout += `${dataStr}`;
   if (/__(SIGINT|SIGTERM) received__/.test(stdout)) {
+    console.log(`[PARENT] Sending kill signal to child process: ${child.pid}`);
     child.kill();
   }
 });
 
+// After the write triggers a restart of the grandchild, the newly spawned second
+// grandchild can post another 'script ready' message before the stdout from the first
+// grandchild is relayed by the watcher and processed by this parent process to kill
+// the watcher. If we write again and trigger another restart, we can
+// end up in an infinite loop and never receive the stdout of the grandchildren in time.
+// Only write once to verify the first grandchild process receives the expected signal.
+// We don't care about the subsequent grandchild processes.
+let written = false;
 child.on('message', (msg) => {
-  if (msg === 'script ready') {
+  console.log(`[MESSAGE]`, msg);
+  if (msg === 'script ready' && !written) {
     writeFileSync(indexPath, indexContents);
+    written = true;
   }
 });