[platform_channels] adds BasicMessageChannel Demo (#484)

platform_channels/test/src/add_pet_details_test.dart

@@ -0,0 +1,37 @@
+// Copyright 2020 The Flutter team. 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/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:platform_channels/src/add_pet_details.dart';
+
+void main() {
+  group('AddPetDetails tests', () {
+    var petList = <Map>[];
+
+    setUpAll(() {
+      BasicMessageChannel<dynamic>('jsonMessageCodecDemo', JSONMessageCodec())
+          .setMockMessageHandler((dynamic message) async {
+        petList.add(message as Map);
+      });
+    });
+
+    testWidgets('Enter pet details', (tester) async {
+      await tester.pumpWidget(MaterialApp(home: AddPetDetails()));
+
+      // Enter the breed of cat.
+      await tester.enterText(find.byType(TextField), 'Persian');
+      // Select cat from the pet type.
+      await tester.tap(find.text('Cat'));
+
+      // Initially the list will be empty.
+      expect(petList, isEmpty);
+      await tester.tap(find.byIcon(Icons.add));
+
+      expect(petList, isNotEmpty);
+      expect(petList.last['breed'], 'Persian');
+    });
+  });
+}