如何模拟/存根 Flutter 平台通道/插件？

Question

我在 Flutter 网站上阅读了 introduction to platform-specific plugins/channels 并浏览了一些简单的插件示例，例如 url_launcher：

// Copyright 2017 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 'dart:async';

import 'package:flutter/services.dart';

const _channel = const MethodChannel('plugins.flutter.io/url_launcher');

/// Parses the specified URL string and delegates handling of it to the
/// underlying platform.
///
/// The returned future completes with a [PlatformException] on invalid URLs and
/// schemes which cannot be handled, that is when [canLaunch] would complete
/// with false.
Future<Null> launch(String urlString) {
  return _channel.invokeMethod(
    'launch',
    urlString,
  );
}

在小部件测试或集成测试中，我如何模拟或存根通道，这样我就不必依赖真实设备（运行 Android 或 iOS），例如实际启动 URL？

Answer 1

您可以使用 setMockMethodCallHandler 为底层方法通道注册一个模拟处理程序：

https://docs.flutter.io/flutter/services/MethodChannel/setMockMethodCallHandler.html

final List<MethodCall> log = <MethodCall>[];

MethodChannel channel = const MethodChannel('plugins.flutter.io/url_launcher');

// Register the mock handler.
channel.setMockMethodCallHandler((MethodCall methodCall) async {
  log.add(methodCall);
});

await launch("http://example.com/");

expect(log, equals(<MethodCall>[new MethodCall('launch', "http://example.com/")]));

// Unregister the mock handler.
channel.setMockMethodCallHandler(null);

Answer 2

MethodChannel#setMockMethodCallHandler 现已弃用并删除。

看起来这是现在要走的路：

import 'package:flutter/services.dart'; 
import 'package:flutter_test/flutter_test.dart';

void mockUrlLauncher() {
  const channel = MethodChannel('plugins.flutter.io/url_launcher');

  handler(MethodCall methodCall) async {
    if (methodCall.method == 'yourMethod') {
      return 42;
    }
    return null;
  }

  TestWidgetsFlutterBinding.ensureInitialized();

  TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
      .setMockMethodCallHandler(channel, handler);
}

详情请见GitHub。

这里是package_info 插件的测试示例供将来参考：

import 'package:flutter/services.dart'; 
import 'package:flutter_test/flutter_test.dart';

void mockPackageInfo() {
  const channel = MethodChannel('plugins.flutter.io/package_info');

  handler(MethodCall methodCall) async {
    if (methodCall.method == 'getAll') {
      return <String, dynamic>{
        'appName': 'myapp',
        'packageName': 'com.mycompany.myapp',
        'version': '0.0.1',
        'buildNumber': '1'
      };
    }
    return null;
  }

  TestWidgetsFlutterBinding.ensureInitialized();

  TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
      .setMockMethodCallHandler(channel, handler);
}

Answer 3

当您创建插件时，系统会自动为您提供默认测试：

void main() {
  const MethodChannel channel = MethodChannel('my_plugin');

  setUp(() {
    channel.setMockMethodCallHandler((MethodCall methodCall) async {
      return '42';
    });
  });

  tearDown(() {
    channel.setMockMethodCallHandler(null);
  });

  test('getPlatformVersion', () async {
    expect(await MyPlugin.platformVersion, '42');
  });
}

让我添加一些关于它的注释：

• 调用setMockMethodCallHandler 允许您绕过实际插件所做的一切并返回您自己的值。
• 您可以使用methodCall.method 来区分方法，它是被调用方法名称的字符串。
• 对于插件创建者，这是一种验证公共 API 名称的方法，但它不会测试 API 的功能。您需要为此使用集成测试。