如何使用 Mockito 在 Flutter 中模拟静态方法？

Question

我有一个文件fetchPosts()，它负责从服务器获取新帖子并将它们存储在本地 sqlite 数据库中。

按照 sqflite doc上的建议，我将单个引用存储到我的数据库中。

这是我的database.dart文件的内容：

import 'dart:async';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';

class DBProvider {
  DBProvider._();
  static final DBProvider db = DBProvider._();

  static Database _database;

  static Future<Database> get database async {
    if (_database != null) return _database;
    // if _database is null, we instantiate it
    _database = await _initDB();
    return _database;
  }

  static Future<Database> _initDB() async {
    final dbPath = await getDatabasesPath();
    String path = join(dbPath, 'demo.db');

    return await openDatabase(path, version: 1, onCreate: _onCreate);
  }

  static Future<String> insert(String table, Map<String, dynamic> values) async { /* insert the record*/ }

  // Other functions like update, delete etc.
}

然后我在我的fetchPosts.dart文件中使用它

import 'dart:convert';
import 'package:http/http.dart' as http;
import '../services/database.dart';

const url = 'https://myapp.herokuapp.com';

Future<void> fetchPosts() {
  final client = http.Client();
  return fetchPostsUsingClient(client);
}

Future<void> fetchPostsUsingClient(http.Client client) async {
  final res = await client.get(url);
  final posts await Post.fromJson(json.decode(response.body));

  for (var i = 0; i < posts.length; i++) {
    await DBProvider.insert('posts', posts[i]);
  }
}

在我的测试，我怎么能verify说DBProvider.insert()已经叫什么？

fetchPosts_test.dart

import 'package:test/test.dart';
import 'package:http/http.dart' as http;
import 'package:mockito/mockito.dart';
import 'package:../services/fetchPosts.dart';

// Create a MockClient using the Mock class provided by the Mockito package.
// Create new instances of this class in each test.
class MockClient extends Mock implements http.Client {}

void main() {
  group('fetchPosts', () {
    test('update local db', () async {
      final client = MockClient();

      // Use Mockito to return a successful response when it calls the provided http.Client.
      when(client.get()).thenAnswer((_) async => http.Response('{"title": "Test"}', 200));

      await fetchPostsWithClient(client);

      verify(/* DBProvider.insert has been called ?*/);
    });
  });
}

Answer 1

这个问题是不久前提出的，但这里有另一个解决方案。您可以重构对该静态函数的调用，以从类“包装器”方法中调用。这是我经常用来模拟对第三方服务的请求的模式。

让我举一个例子。为了简单起见，我们假设 Engine 有 3 个需要模拟的静态方法：brake()、accelerate() 和 speed()。

class Car {
    int currentSpeed;

    void accelerateTo(int speed) {
         while(currentSpeed > speed) {
              Engine.brake();
              currentSpeed = Engine.speed();
         }
         while(currentSpeed < speed) {
              Engine.accelerate();
              currentSpeed = Engine.speed();
         }
    }
}

现在您想要模拟对引擎的所有调用，为此我们可以将代码重构为：

class Car {
    int currentSpeed;

    void accelerateTo(int speed) {
         while(currentSpeed > speed) {
              brake();
              currentSpeed = speed();
         }
         while(currentSpeed < speed) {
              accelerate();
              currentSpeed = speed();
         }
    }

    /// wrapper to mock Engine calls during test
    void brake() {
        Engine.brake();
    }

    /// wrapper to mock Engine calls during test
    int speed() {
        Engine.speed();
    }

    /// wrapper to mock Engine calls during test
    void accelerate() {
        Engine.accelerate();
    }

}

在集成测试中，您现在可以模拟直接与静态方法交互的 3 个方法，但现在您可以测试您的 main 方法。虽然您还可以在这里重构 Engine 类本身，但该类通常位于第三方服务中。

这个例子并非基于大众汽车丑闻；）。

Answer 2

最终，我不得不重写我的database.dart以使其可测试/可模拟。
这是新文件：

import 'dart:async';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';

class DBProvider {
  static final DBProvider _singleton = DBProvider._internal();

  factory DBProvider() {
    return _singleton;
  }

  DBProvider._internal();

  static Database _db;

  static Future<Database> _getDatabase() async {
    if (_db != null) return _db;
    // if _database is null, we instantiate it
    _db = await _initDB();
    return _db;
  }

  static Future<Database> _initDB() async {
    final dbPath = await getDatabasesPath();
    String path = join(dbPath, 'demo.db');

    return openDatabase(path, version: 1, onCreate: _onCreate);
  }

  Future<String> insert(String table, Map<String, dynamic> values) async {
    final db = await _getDatabase();
    return db.insert(table, values);
  }

  // ...
}

现在我可以使用与 http.Client 相同的技巧。谢谢@RémiRousselet