Fix plugin template app's tests (#39080)

* Fix plugin template

* Add test of plugin template working

dev/devicelab/lib/tasks/plugin_tests.dart

@@ -23,8 +23,8 @@ TaskFunction combine(List<TaskFunction> tasks) {
   };
 }
 
-/// Defines task that creates new Flutter project, adds a plugin, and then
-/// builds the specified [buildTarget].
+/// Defines task that creates new Flutter project, adds a local and remote
+/// plugin, and then builds the specified [buildTarget].
 class PluginTest {
   PluginTest(this.buildTarget, this.options);
 
@@ -32,19 +32,32 @@ class PluginTest {
   final List<String> options;
 
   Future<TaskResult> call() async {
-    section('Create Flutter project');
-    final Directory tempDir = Directory.systemTemp.createTempSync('flutter_devicelab_plugin_test.');
+    final Directory tempDir =
+        Directory.systemTemp.createTempSync('flutter_devicelab_plugin_test.');
     try {
-      final FlutterProject project = await FlutterProject.create(tempDir, options);
+      section('Create plugin');
+      final _FlutterProject plugin = await _FlutterProject.create(
+          tempDir, options,
+          name: 'plugintest', template: 'plugin');
+      section('Test plugin');
+      await plugin.test();
+      section('Create Flutter app');
+      final _FlutterProject app = await _FlutterProject.create(tempDir, options,
+          name: 'plugintestapp', template: 'app');
       try {
         if (buildTarget == 'ios')
-          await prepareProvisioningCertificates(project.rootPath);
-        section('Add plugin');
-        await project.addPlugin('path_provider');
-        section('Build');
-        await project.build(buildTarget);
+          await prepareProvisioningCertificates(app.rootPath);
+        section('Add plugins');
+        await app.addPlugin('plugintest',
+            pluginPath: path.join('..', 'plugintest'));
+        await app.addPlugin('path_provider');
+        section('Build app');
+        await app.build(buildTarget);
+        section('Test app');
+        await app.test();
       } finally {
-        await project.delete();
+        await plugin.delete();
+        await app.delete();
       }
       return TaskResult.success(null);
     } catch (e) {
@@ -55,32 +68,48 @@ class PluginTest {
   }
 }
 
-class FlutterProject {
-  FlutterProject(this.parent, this.name);
+class _FlutterProject {
+  _FlutterProject(this.parent, this.name);
 
   final Directory parent;
   final String name;
 
-  static Future<FlutterProject> create(Directory directory, List<String> options) async {
+  String get rootPath => path.join(parent.path, name);
+
+  Future<void> addPlugin(String plugin, {String pluginPath}) async {
+    final File pubspec = File(path.join(rootPath, 'pubspec.yaml'));
+    String content = await pubspec.readAsString();
+    final String dependency =
+        pluginPath != null ? '$plugin:\n    path: $pluginPath' : '$plugin:';
+    content = content.replaceFirst(
+      '\ndependencies:\n',
+      '\ndependencies:\n  $dependency\n',
+    );
+    await pubspec.writeAsString(content, flush: true);
+  }
+
+  Future<void> test() async {
+    await inDirectory(Directory(rootPath), () async {
+      await flutter('test');
+    });
+  }
+
+  static Future<_FlutterProject> create(
+      Directory directory, List<String> options,
+      {String name, String template}) async {
     await inDirectory(directory, () async {
       await flutter(
         'create',
-        options: <String>['--template=app', '--org', 'io.flutter.devicelab', ...options, 'plugintest'],
+        options: <String>[
+          '--template=$template',
+          '--org',
+          'io.flutter.devicelab',
+          ...options,
+          name
+        ],
       );
     });
-    return FlutterProject(directory, 'plugintest');
-  }
-
-  String get rootPath => path.join(parent.path, name);
-
-  Future<void> addPlugin(String plugin) async {
-    final File pubspec = File(path.join(rootPath, 'pubspec.yaml'));
-    String content = await pubspec.readAsString();
-    content = content.replaceFirst(
-      '\ndependencies:\n',
-      '\ndependencies:\n  $plugin:\n',
-    );
-    await pubspec.writeAsString(content, flush: true);
+    return _FlutterProject(directory, name);
   }
 
   Future<void> build(String target) async {
@@ -93,11 +122,11 @@ class FlutterProject {
     if (Platform.isWindows) {
       // A running Gradle daemon might prevent us from deleting the project
       // folder on Windows.
-      await exec(
-        path.absolute(path.join(rootPath, 'android', 'gradlew.bat')),
-        <String>['--stop'],
-        canFail: true,
-      );
+      final String wrapperPath =
+          path.absolute(path.join(rootPath, 'android', 'gradlew.bat'));
+      if (File(wrapperPath).existsSync()) {
+        await exec(wrapperPath, <String>['--stop'], canFail: true);
+      }
       // TODO(ianh): Investigating if flakiness is timing dependent.
       await Future<void>.delayed(const Duration(seconds: 10));
     }

packages/flutter_tools/templates/plugin/test/projectName_test.dart.tmpl

@@ -5,6 +5,8 @@ import 'package:{{projectName}}/{{projectName}}.dart';
 void main() {
   const MethodChannel channel = MethodChannel('{{projectName}}');
 
+  TestWidgetsFlutterBinding.ensureInitialized();
+
   setUp(() {
     channel.setMockMethodCallHandler((MethodCall methodCall) async {
       return '42';