Flutter：SharedPreferences 包装类测试返回 null

Question

我有一个问题，我有以下问题

Preferences.dart

首选项.dart

/// Wrapper class for the shared preferences.
class Preferences {
  Preferences({required SharedPreferences sharedPreferences})
      : _sharedPreferences = sharedPreferences;
  final SharedPreferences _sharedPreferences;

  /// Writes the [value] to the shared preferences.
  Future<bool> write({required String key, required String value}) =>
      _sharedPreferences.setString(key, value);

  /// Writes the list of [values] to the shared preferences.
  Future<bool> writeList({required String key, required List<String> values}) =>
      _sharedPreferences.setStringList(key, values);

  /// Reads the value from the shared preferences.
  String? read({required String key}) => _sharedPreferences.getString(key);

  /// Reads the list of values from the shared preferences.
  List<String>? readList({required String key}) =>
      _sharedPreferences.getStringList(key);

  /// Clears the shared preferences.
  Future<bool> clearAll() => _sharedPreferences.clear();

  /// Clears the shared preferences for the given [key].
  Future<bool> clear({required String key}) => _sharedPreferences.remove(key);
}

在尝试创建相应的测试类时，我总是收到以下错误：

type 'Null' is not a subtype of type 'Future<bool>' test/mocks/mocks.dart 8:7                            MockPreferences.write test/domain/preferences/preferences_test.dart 19:26  main.<fn>

目前这是我使用的测试类：

import 'package:flutter_test/flutter_test.dart';
import 'package:garrapata_app/domain/preferences/preferences.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:mockito/mockito.dart';
import '../../mocks/mocks.dart';

void main() {
  TestWidgetsFlutterBinding.ensureInitialized();

  late Preferences mockPreferences;

  setUpAll(() async {
    SharedPreferences.setMockInitialValues({'demo': 'demo'});
    mockPreferences = MockPreferences();
  });

  test('demo', () {
    when(mockPreferences.write(key: 'demo', value: 'demo')).thenAnswer((_) async => true);
    expect(mockPreferences.write(key: 'demo', value: 'demo'), completion(true));
  });
}

我不确定为什么一直为空，模拟值的初始化已解决并且分配已完成。

Answer 1

你没有等到

SharedPreferences

set 方法得到完整的结果

  Future<bool> write({required String key, required String value}) =>
      _sharedPreferences.setString(key, value);

修复

  Future<bool> write({required String key, required String value}) =>
     await _sharedPreferences.setString(key, value);

await

对于set方法，任何

SharedPreferences

set方法都需要等待。

希望对您有帮助。