test: add graceful handling of test-debugger-pid flakes

test/common/debugger.js

@@ -180,10 +180,14 @@ function startCLI(args, flags = [], spawnOpts = {}, opts = { randomPort: true })
     },
 
     quit() {
-      return new Promise((resolve) => {
-        child.stdin.end();
-        child.on('close', resolve);
+      const { promise, resolve } = Promise.withResolvers();
+      child.stdin.end();
+      const t = setTimeout(() => child.kill('SIGKILL'), TIMEOUT);
+      child.on('close', (code) => {
+        clearTimeout(t);
+        resolve(code);
       });
+      return promise;
     },
   };
 }

test/sequential/test-debugger-pid.js

@@ -7,11 +7,35 @@ const fixtures = require('../common/fixtures');
 const startCLI = require('../common/debugger');
 
 const assert = require('assert');
+const net = require('net');
 const { spawn } = require('child_process');
 
 const script = fixtures.path('debugger', 'alive.js');
 
+// The -p <pid> attach mode uses the default inspector port (9229).
+// If that port is already in use, the test will hang. Check first and skip.
+function checkPort(port) {
+  const { promise, resolve, reject } = Promise.withResolvers();
+  const server = net.createServer();
+  server.once('error', reject);
+  server.listen(port, '127.0.0.1', () => server.close(resolve));
+  return promise;
+}
+
 (async () => {
+  try {
+    await checkPort(9229);
+  } catch (e) {
+    // In the typical case, this test runs in sequential set and depends on
+    // nothing else bound to port 9229. However, if there's some other failure
+    // that causes an orphaned process to be left running on port 9229, this
+    // test was hanging and timing out. Let's arrange to skip instead of hanging.
+    if (e.code === 'EADDRINUSE') {
+      common.skip('Port 9229 is already in use');
+    }
+    throw e;
+  }
+
   const target = spawn(process.execPath, [script]);
   const cli = startCLI(['-p', `${target.pid}`], [], {}, { randomPort: false });
 
@@ -20,12 +44,12 @@ const script = fixtures.path('debugger', 'alive.js');
     await cli.command('sb("alive.js", 3)');
     await cli.waitFor(/break/);
     await cli.waitForPrompt();
-    assert.match(
-      cli.output,
-      /> 3 {3}\+\+x;/,
-      'marks the 3rd line');
+    assert.match(cli.output, /> 3 {3}\+\+x;/, 'marks the 3rd line');
   } finally {
-    await cli.quit();
     target.kill();
+    await Promise.race([
+      cli.quit(),
+      new Promise((resolve) => setTimeout(resolve, 5000)),
+    ]);
   }
 })().then(common.mustCall());