test: capture stack trace in debugger timeout errors

Otherwise when the expected prompt does not show up in the
session and the debugger tests time out, there is not enough
information to figure out exactly which line in the test
is causing the timeout.

Author: joyeecheung

test/common/debugger.js

@@ -88,12 +88,14 @@ function startCLI(args, flags = [], spawnOpts = {}, opts = { randomPort: true })
           reject(new Error(message));
         }
 
+        // Capture stack trace here to show where waitFor was called from when
+        // it times out.
+        const timeoutErr = new Error(`Timeout (${TIMEOUT}) while waiting for ${pattern}`);
+        Error.captureStackTrace(timeoutErr, this.waitFor);
         const timer = setTimeout(() => {
           tearDown();
-          reject(new Error([
-            `Timeout (${TIMEOUT}) while waiting for ${pattern}`,
-            `found: ${this.output}`,
-          ].join('; ')));
+          err.output = this.output;
+          reject(err);
         }, TIMEOUT);
 
         function tearDown() {