feat：参照研听的基础工程

packages/flutter_paid/test/flutter_paid_method_channel_test.dart

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+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_paid/flutter_paid_method_channel.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  MethodChannelFlutterPaid platform = MethodChannelFlutterPaid();
+  const MethodChannel channel = MethodChannel('flutter_paid');
+
+  setUp(() {
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(
+      channel,
+      (MethodCall methodCall) async {
+        return '42';
+      },
+    );
+  });
+
+  tearDown(() {
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(channel, null);
+  });
+
+  test('getPlatformVersion', () async {
+    expect(await platform.getPlatformVersion(), '42');
+  });
+}

packages/flutter_paid/test/flutter_paid_test.dart

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+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_paid/flutter_paid.dart';
+import 'package:flutter_paid/flutter_paid_platform_interface.dart';
+import 'package:flutter_paid/flutter_paid_method_channel.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+class MockFlutterPaidPlatform
+    with MockPlatformInterfaceMixin
+    implements FlutterPaidPlatform {
+
+  @override
+  Future<String?> getPlatformVersion() => Future.value('42');
+}
+
+void main() {
+  final FlutterPaidPlatform initialPlatform = FlutterPaidPlatform.instance;
+
+  test('$MethodChannelFlutterPaid is the default instance', () {
+    expect(initialPlatform, isInstanceOf<MethodChannelFlutterPaid>());
+  });
+
+  test('getPlatformVersion', () async {
+    FlutterPaid flutterPaidPlugin = FlutterPaid();
+    MockFlutterPaidPlatform fakePlatform = MockFlutterPaidPlatform();
+    FlutterPaidPlatform.instance = fakePlatform;
+
+    expect(await flutterPaidPlugin.getPlatformVersion(), '42');
+  });
+}