Angular17升级至19后TestBed导入独立组件失效，强制设true生效原因？

问题场景 #

将应用从Angular 17升级至Angular 19（19.0.6）及Nx20版本后，使用TestBed测试包含独立组件的非独立组件时出现报错。

相关代码 #

非独立组件ConnectionComponent #

@Component({
  templateUrl: './connection.component.html',
  changeDetection: ChangeDetectionStrategy.OnPush,
  standalone: false
})
export class ConnectionComponent implements OnInit {...

独立组件FeatureConsentsComponent（原代码） #

@Component({
    selector: 'consents',
    templateUrl: './consents.component.html',
    changeDetection: ChangeDetectionStrategy.OnPush,
    imports: [NgIf, CheckBoxModule, LayoutModule, NgFor, AsyncPipe, TranslateModule],
    providers: [ConsentsHttpService, addDynamicComponentProviders(ConsentsErrorsProvider)]
})

测试代码 #

beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [FakesModule, CoreTranslationTestingModule, MockComponent(FeatureConsentsComponent)],
      declarations: [
        ConnectionComponent,
        MockComponent(ButtonComponent),
        MockComponents(MotivationBlockComponent, MotivationBlockItemComponent)
      ],
      providers: [
        provideMockStore(),
        provideDummyTokens(),
      ]
    });
    fixture = TestBed.createComponent(ConnectionComponent);
    component = fixture.componentInstance;
  });

报错信息 #

Unexpected "MockOfFeatureConsentsComponent" found in the "declarations" array of the "TestBed.configureTestingModule" call, "MockOfFeatureConsentsComponent" is marked as standalone and can't be declared in any NgModule - did you intend to import it instead (by adding it to the "imports" array)?

问题原因 #

1. Angular 19收紧独立组件声明规则
   Angular 17中，组件只要配置了imports数组，会自动被隐式识别为独立组件（相当于standalone: true）；但Angular 19取消了这个隐式逻辑，必须显式声明standalone: true，即使组件包含imports数组，否则Angular不会将其认定为合法的独立组件。

2. Mock组件生成逻辑与TestBed校验的冲突
   你使用的Mock库（如ng-mocks）在生成FeatureConsentsComponent的Mock时，会检测到原组件配置了imports数组，自动将Mock组件标记为standalone: true。但原组件未显式声明standalone: true，导致TestBed在解析配置时出现矛盾：Mock组件是独立组件（必须放在imports），但原组件的不完整元数据让TestBed误判了处理逻辑，最终触发报错。

3. 显式声明standalone: true的修复原理
   当给FeatureConsentsComponent加上standalone: true后，原组件的元数据与Mock组件的属性完全匹配，TestBed能正确识别Mock组件为独立组件，放在imports数组中符合Angular的规则，因此测试可以正常运行。

内容的提问来源于stack exchange，提问作者Pak