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我试图测试注入它的父组件作为组件：角4 +噶测试组件
constructor(@Host() app: ParentComponent) {
...
}当我运行测试，我得到以下信息：
错误：无提供者为父级
我已经有我包括父组件和子组件中使用的所有依赖项。我是否需要做任何特定的事情来注入主机组件？
这里是我完整的测试：
describe('ChildComponent: Component',() => {
\t //declare the component
\t let comp: ChildComponent;
\t let ca: ComponentFixture<ChildComponent>;
\t //setup
\t //first the async call to compile all the external templates
\t beforeEach(async(() => {
\t \t TestBed.configureTestingModule({
\t \t \t imports: [
\t \t \t \t ...
\t \t \t ],
\t \t \t declarations: [
\t \t \t \t ParentComponent,
\t \t \t \t ChildComponent
\t \t \t ],
\t \t \t providers: [
\t \t \t \t ...
\t \t \t ]
\t \t })
\t \t .compileComponents();
\t }));
\t //then the sync call to create the instance
\t beforeEach(() => {
\t \t
\t \t ca = TestBed.createComponent(ChildComponent);
\t \t comp = ca.componentInstance;
\t \t ca.detectChanges();
\t });
\t afterEach(() => {
\t \t comp = null;
\t \t ca = null;
\t });
\t //define the tests
\t it('should have items...',() => {
\t \t let count: number = comp.someArray.length;
\t \t expect(count).toBeGreaterThan(0); \t \t
\t });
});