Add a hot reload test that modifies code and verifies it executes (#23725)

packages/flutter_tools/test/integration/hot_reload_test.dart

@@ -2,19 +2,21 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:vm_service_client/vm_service_client.dart';
 
 import '../src/common.dart';
-import 'test_data/basic_project.dart';
+import 'test_data/hot_reload_project.dart';
 import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
   group('hot', () {
     Directory tempDir;
-    final BasicProject _project = BasicProject();
+    final HotReloadProject _project = HotReloadProject();
     FlutterTestDriver _flutter;
 
     setUp(() async {
@@ -33,6 +35,19 @@ void main() {
       await _flutter.hotReload();
     });
 
+    test('newly added code executes during reload', () async {
+      await _flutter.run();
+      _project.uncommentHotReloadPrint();
+      final StringBuffer stdout = StringBuffer();
+      final StreamSubscription<String> sub = _flutter.stdout.listen(stdout.writeln);
+      try {
+            await _flutter.hotReload();
+            expect(stdout.toString(), contains('(((((RELOAD WORKED)))))'));
+      } finally {
+        await sub.cancel();
+      }
+    });
+
     test('restart works without error', () async {
       await _flutter.run();
       await _flutter.hotRestart();

packages/flutter_tools/test/integration/test_data/hot_reload_project.dart

@@ -0,0 +1,54 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_tools/src/base/file_system.dart';
+
+import '../test_utils.dart';
+import 'test_project.dart';
+
+class HotReloadProject extends TestProject {
+  @override
+  final String pubspec = '''
+  name: test
+  environment:
+    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+
+  dependencies:
+    flutter:
+      sdk: flutter
+  ''';
+
+  @override
+  final String main = r'''
+  import 'package:flutter/material.dart';
+
+  void main() => runApp(new MyApp());
+
+  class MyApp extends StatelessWidget {
+    @override
+    Widget build(BuildContext context) {
+      // Do not remove this line, it's uncommented by a test to verify that hot
+      // reloading worked.
+      // printHotReloadWorked();
+
+      return new MaterialApp( // BREAKPOINT
+        title: 'Flutter Demo',
+        home: new Container(),
+      );
+    }
+  }
+
+  printHotReloadWorked() {
+    // The call to this function is uncommented by a test to verify that hot
+    // reloading worked.
+    print('(((((RELOAD WORKED)))))');
+  }
+  ''';
+
+  void uncommentHotReloadPrint() {
+    final String newMainContents = main.replaceAll(
+        '// printHotReloadWorked();', 'printHotReloadWorked();');
+    writeFile(fs.path.join(dir.path, 'lib', 'main.dart'), newMainContents);
+  }
+}

packages/flutter_tools/test/integration/test_driver.dart

@@ -42,6 +42,7 @@ class FlutterTestDriver {
 
   VMServiceClient vmService;
   String get lastErrorInfo => _errorBuffer.toString();
+  Stream<String> get stdout => _stdout.stream;
   int get vmServicePort => _vmServicePort;
   bool get hasExited => _hasExited;