[Angular中的单元测试时，在Karma中显示未捕获的TypeError

Question

假设我有一个名为testService的服务，其中包含函数getData。我也有将服务注入其中的组件（例如A）。

export class A implements OnInit,OnDestroy{
    saveObj;

    constructor(public service:testService){

    }

    ngOnDestroy(){
      if(this.saveObj) this.saveObj.unsubscribe();
    }

    ngOnInit(){
        this.saveObj = this.service.getData.subscribe(res => {
            this.func(res);
        },
        err => {
            console.log("Error Occured");
            this.saveObj.unsubscribe();
        });
    }

    private func(result: any){
        // Some code
    }
}

现在我正在对此组件进行单元测试。问题是在某些情况下，它会引发错误：

Uncaught TypeError: _this.saveObj.unsubscribe is not a function thrown

spec.ts的代码段：

// testServiceStub is just a mock of testService. 

beforeEach(async(()=>{
    testServiceStub = jasmine.createSpyObj(['getData']);

    TestBed.configureTestingModule({
        declarations : [A],
        schemas : [NO_ERRORS_SCHEMA],
        providers : [
            { provide : testService, useValue: testServiceStub }
        ]
    }).compileComponents();
}))

beforeEach(async(()=>{
    fixture = TestBed.createComponent(A);
    component = fixture.componentInstance;
}))

it('checks whether error is handled or not',()=>{
    spyOn(console,'log');
    testServiceStub.getData.and.returnValue(throwError({status:404})); 
    fixture.detectChanges();
    expect(console.log).toHaveBeenCalled(); // shows the TypeError
})


it('checks whether value is handled or not',()=>{
    testServiceStub.getData.and.returnValue(of(mockData)); // some mock data
    fixture.detectChanges();
    expect(component.func).toHaveBeenCalled();  // also shows the TypeError
})

我也将此链接称为unsubscribe is not a function on an observable。但是问题是它在某些情况下也可以使用，并且没有显示错误。

[请帮助我找出原因和可能的情况。

UPD：添加了onDestroy生命周期挂钩

Answer 1

根据@Amit Chigadani的建议

export class A implements OnInit,OnDestroy{
    saveObj;

    constructor(public service:testService){

    }

    ngOnDestroy(){
      if(this.saveObj) 
             this.saveObj.unsubscribe();
    }

    ngOnInit(){
        this.saveObj = this.service.getData.subscribe(res => {
            this.func(res);
        },
        err => {
            console.log("Error Occured");
        });
    }

    private func(result: any){
        // Some code
    }
}