test: harden debugger prompt test

Use a long-lived debugger target and assert that the prompt is received
before sending the exit command.

Handle child exit and timeout failures explicitly instead of leaving the
test hanging when startup does not produce a prompt.

Signed-off-by: Matteo Collina <hello@matteocollina.com>

Author: mcollina

test/sequential/test-debug-prompt.js

@@ -2,17 +2,45 @@
 
 const common = require('../common');
 common.skipIfInspectorDisabled();
+const assert = require('assert');
+const fixtures = require('../common/fixtures');
 const spawn = require('child_process').spawn;
 
-const proc = spawn(process.execPath, ['inspect', 'foo']);
+const proc = spawn(process.execPath, [
+  'inspect', fixtures.path('debugger', 'alive.js'),
+]);
 proc.stdout.setEncoding('utf8');
 
-let needToSendExit = true;
+const TIMEOUT = common.platformTimeout(10_000);
 let output = '';
-proc.stdout.on('data', (data) => {
-  output += data;
-  if (output.includes('debug> ') && needToSendExit) {
-    proc.stdin.write('.exit\n');
-    needToSendExit = false;
-  }
-});
+let promptSeen = false;
+
+(async () => {
+  await new Promise((resolve, reject) => {
+    const timer = setTimeout(() => {
+      proc.kill();
+      reject(new Error(`Timed out waiting for the debugger prompt; output: ${output}`));
+    }, TIMEOUT);
+
+    proc.stdout.on('data', (data) => {
+      output += data;
+      if (output.includes('debug> ') && !promptSeen) {
+        promptSeen = true;
+        proc.stdin.end('.exit\n');
+      }
+    });
+
+    proc.once('error', reject);
+    proc.once('close', common.mustCall((code, signal) => {
+      clearTimeout(timer);
+      if (!promptSeen) {
+        reject(new Error(
+          `Debugger exited before showing the prompt (code ${code}, signal ${signal}); ` +
+          `output: ${output}`));
+        return;
+      }
+      assert.strictEqual(code, 0);
+      resolve();
+    }));
+  });
+})().then(common.mustCall());