Mocktail封装stub方法报No method stub was called from when()错误

我正在使用 mocktail 0.3.0 包测试HttpAdapter类的request()方法，该方法会调用http包中Client类的post()方法。
初始业务代码如下：

import 'dart:io';
import 'package:http/http.dart';

class HttpAdapter {
  static const headers = {
    HttpHeaders.contentTypeHeader: 'application/json',
    HttpHeaders.acceptHeader: 'application/json',
  };

  final Client client;

  HttpAdapter(this.client);

  Future<void> request({
    required String url,
    required String method,
    HttpClientBody? body,
  }) async {
    await client.post(Uri.parse(url), headers: HttpAdapter.headers);
  }
}

class ClientSpy extends Mock implements Client {
  void mockPost(String url) {
    when(() => post(
          Uri.parse(url),
          headers: any(named: 'headers'),
        )).thenAnswer(
      (_) async => Response('{}', HttpStatus.ok),
    );
  }
}

直接在测试中编写when打桩逻辑时，用例可正常运行：

void main() {
 test('Should call post() with correct parameters', () async {
   // Arrange
   final client = ClientSpy();
   final sut = HttpAdapter(client);

   when(() => client.post(
         Uri.parse(url),
         headers: HttpAdapter.headers,
       )).thenAnswer(
     (_) async => Response('{}', HttpStatus.ok),
   );
   // Act
   await sut.request(url: url, method: method);
   // Assert
   verify(() => client.post(
         Uri.parse(url),
         headers: HttpAdapter.headers,
       ));
  });
}

但将when()打桩语句封装为mockPost()方法调用时，测试会抛出错误：

Bad state: No method stub was called from within 'when()'. Was a real method called, or perhaps an extension method?

对应报错的测试代码如下：

void main() {
 test('Should call post() with correct parameters', () async {
   // Arrange
   final client = ClientSpy();
   final sut = HttpAdapter(client);

   client.mockPost();
   // Act
   await sut.request(url: url, method: method);
   // Assert
   verify(() => client.post(
         Uri.parse(url),
         headers: HttpAdapter.headers,
       ));
  });
}

代码存在两个核心问题：

• 方法调用绑定错误：http包自带顶层post()函数，在ClientSpy的mockPost方法中直接写post(...)时，Dart会优先解析为调用http包的顶层真实网络请求方法，而非当前mock实例的post()实例方法。mocktail依赖拦截mock实例的方法调用来完成打桩，真实方法调用不会被拦截，因此抛出No method stub was called错误。
• 参数缺失：mockPost方法定义了必填的String url参数，但测试中调用client.mockPost()时未传入该参数，本身不符合方法调用要求。

1. 修改ClientSpy的打桩逻辑，给被mock的post方法加上this.前缀，强制指定调用当前mock实例的方法：

class ClientSpy extends Mock implements Client {
  void mockPost(String url) {
    // 增加this.前缀，避免误调用顶层post函数
    when(() => this.post(
          Uri.parse(url),
          headers: any(named: 'headers'),
        )).thenAnswer(
      (_) async => Response('{}', HttpStatus.ok),
    );
  }
}

2. 测试中调用mockPost时，传入对应的测试url参数：

void main() {
  // 提前定义测试常量
  const testUrl = 'https://example.com/test';
  const testMethod = 'post';

 test('Should call post() with correct parameters', () async {
   // Arrange
   final client = ClientSpy();
   final sut = HttpAdapter(client);
   // 传入必填的url参数
   client.mockPost(testUrl);
   // Act
   await sut.request(url: testUrl, method: testMethod);
   // Assert
   verify(() => client.post(
         Uri.parse(testUrl),
         headers: HttpAdapter.headers,
       ));
  });
}

修改后测试即可正常运行。 #

内容的提问来源于stack exchange，提问作者Eyder Rios