Serve DevTools when running flutter test (#123607)

Also clean up messaging output by `flutter test` when `--start-paused` is provided.

packages/flutter_tools/lib/src/test/flutter_tester_device.dart

@@ -21,6 +21,7 @@ import '../convert.dart';
 import '../device.dart';
 import '../globals.dart' as globals;
 import '../project.dart';
+import '../resident_runner.dart';
 import '../vmservice.dart';
 
 import 'font_config_manager.dart';
@@ -72,6 +73,7 @@ class FlutterTesterTestDevice extends TestDevice {
 
   Process? _process;
   HttpServer? _server;
+  DevtoolsLauncher? _devToolsLauncher;
 
   /// Starts the device.
   ///
@@ -163,9 +165,11 @@ class FlutterTesterTestDevice extends TestDevice {
             debuggingOptions.hostVmServicePort == detectedUri.port);
 
         Uri? forwardingUri;
+        DartDevelopmentService? dds;
+
         if (debuggingOptions.enableDds) {
           logger.printTrace('test $id: Starting Dart Development Service');
-          final DartDevelopmentService dds = await startDds(
+          dds = await startDds(
             detectedUri,
             uriConverter: uriConverter,
           );
@@ -193,10 +197,10 @@ class FlutterTesterTestDevice extends TestDevice {
         }));
 
         if (debuggingOptions.startPaused && !machine!) {
-          logger.printStatus('The test process has been started.');
-          logger.printStatus('You can now connect to it using vmService. To connect, load the following Web site in your browser:');
-          logger.printStatus('  $forwardingUri');
-          logger.printStatus('You should first set appropriate breakpoints, then resume the test in the debugger.');
+          logger.printStatus('The Dart VM service is listening on $forwardingUri');
+          await _startDevTools(forwardingUri, dds);
+          logger.printStatus('');
+          logger.printStatus('The test process has been started. Set any relevant breakpoints and then resume the test in the debugger.');
         }
         _gotProcessVmServiceUri.complete(forwardingUri);
       },
@@ -215,6 +219,9 @@ class FlutterTesterTestDevice extends TestDevice {
     logger.printTrace('test $id: Terminating flutter_tester process');
     _process?.kill(io.ProcessSignal.sigkill);
 
+    logger.printTrace('test $id: Shutting down DevTools server');
+    await _devToolsLauncher?.close();
+
     logger.printTrace('test $id: Shutting down test harness socket server');
     await _server?.close(force: true);
     await finished;
@@ -261,6 +268,29 @@ class FlutterTesterTestDevice extends TestDevice {
     );
   }
 
+  Future<void> _startDevTools(Uri forwardingUri, DartDevelopmentService? dds) async {
+    _devToolsLauncher = DevtoolsLauncher.instance;
+    logger.printTrace('test $id: Serving DevTools...');
+    final DevToolsServerAddress? devToolsServerAddress = await _devToolsLauncher?.serve();
+
+    if (devToolsServerAddress == null) {
+      logger.printTrace('test $id: Failed to start DevTools');
+      return;
+    }
+    await _devToolsLauncher?.ready;
+    logger.printTrace('test $id: DevTools is being served at ${devToolsServerAddress.uri}');
+
+    // Notify the DDS instance that there's a DevTools instance available so it can correctly
+    // redirect DevTools related requests.
+    dds?.setExternalDevToolsUri(devToolsServerAddress.uri!);
+
+    final Uri devToolsUri = devToolsServerAddress.uri!.replace(
+      // Use query instead of queryParameters to avoid unnecessary encoding.
+      query: 'uri=$forwardingUri',
+    );
+    logger.printStatus('The Flutter DevTools debugger and profiler is available at: $devToolsUri');
+  }
+
   /// Binds an [HttpServer] serving from `host` on `port`.
   ///
   /// Only intended to be overridden in tests.

packages/flutter_tools/test/integration.shard/test_test.dart

@@ -222,7 +222,7 @@ void main() {
       final Completer<Uri> completer = Completer<Uri>();
       final RegExp vmServiceUriRegExp = RegExp(r'((http)?:\/\/)[^\s]+');
       sub = process.stdout.transform(utf8.decoder).listen((String e) {
-        if (vmServiceUriRegExp.hasMatch(e)) {
+        if (!completer.isCompleted && vmServiceUriRegExp.hasMatch(e)) {
           completer.complete(Uri.parse(vmServiceUriRegExp.firstMatch(e)!.group(0)!));
         }
       });
@@ -237,6 +237,31 @@ void main() {
       process.kill();
     }
   });
+
+  testWithoutContext('flutter test should serve DevTools', () async {
+    late final Process process;
+    late final StreamSubscription<String> sub;
+    try {
+      process = await _runFlutterTestConcurrent('trivial', automatedTestsDirectory, flutterTestDirectory,
+        extraArguments: const <String>['--start-paused']);
+      final Completer<Uri> completer = Completer<Uri>();
+      final RegExp devToolsUriRegExp = RegExp(r'The Flutter DevTools debugger and profiler is available at: (http://[^\s]+)');
+      sub = process.stdout.transform(utf8.decoder).listen((String e) {
+        if (!completer.isCompleted && devToolsUriRegExp.hasMatch(e)) {
+          completer.complete(Uri.parse(devToolsUriRegExp.firstMatch(e)!.group(1)!));
+        }
+      });
+      final Uri devToolsUri = await completer.future;
+      final HttpClient client = HttpClient();
+      final HttpClientRequest request = await client.getUrl(devToolsUri);
+      final HttpClientResponse response = await request.close();
+      final String content = await response.transform(utf8.decoder).join();
+      expect(content.contains('DevTools'), true);
+    } finally {
+      await sub.cancel();
+      process.kill();
+    }
+  });
 }
 
 Future<void> _testFile(