instruction-context.component.spec.ts
    let instructionService: InstructionsService;
    let mockInstructionService:  = {
    instruction: new BehaviorSubject<any>({}).asObservable(),
    applyInstruction: () => {},
    };
    let expectedInstructions = {[]}// object with some expected data
    beforeEach(
    waitForAsync(() => {
      TestBed.configureTestingModule({
        declarations: [InstructionContextComponent],
        imports: [HttpClientTestingModule],
        providers: [
          { provide: InstructionsService, useValue: mockInstructionService},
          HttpService
        ]
      }).compileComponents();
    })
    );
   
    beforeEach(() => {
        fixture = TestBed.createComponent(InstructionContextComponent);
        instructionService = TestBed.inject(InstructionsService);
        component = fixture.componentInstance;
        fixture.detectChanges();
      });
    
    
      describe('ngOninit', () => {
        let instrcutionServiceSpyApplyInstruction;
        beforeEach(() => {
          instrcutionServiceSpyApplyInstruction = spyOn(instructionService, 'applyInstruction');
          spyOn(instructionService , 'instruction' as any).and.returnValue(of(expectedInstructions));
        });
    it('should create', () => {
      // 断言
      expect(component).toBeTruthy();
    });
    it('should apply correct state when mode is "create" and locationData is present', 
       fakeAsync(() => {
       // 准备
       component.mode = 'create';
       component['locationData'] = [{ id: '1', name: 'Node 1' }] as any;
       // 执行
       component.ngOnInit();
       tick(100);
       // 断言
       expect(clearInterval).toHaveBeenCalled();
       expect(instrcutionServiceSpyApplyInstruction ).toHaveBeenCalled();
       }));
     })
instructionService.ts
    public instruction: BehaviorSubject<Instructions>;
    
    set instructions(){
      let state
      // 设置一些状态值
      this.instruction.next({
          ...state
      });
    }
instruction-context.component.ts
    ngOninit(){
    
    this.instructionsService.instruction.subscribe((instruction: IInstruction) => {
          this.instruction = instruction;
          this.instructionLevel = this.instruction && this.instruction['level'];
          this.instructionContext = this.instruction && this.instruction['context'];
          if (this.instructionContext) {
            this.locationData = this.instructionContext['locationData'];
            if (this.instructionContext['types'] && this.instructionContext['types'][this.mode]) {
              this.filterNodes = this.instructionContext['types'][this.mode][
                'filterNodes'
              ];
              this.tree = this.instructionContext['types'][this.mode]['treeData'];
    
              this.selectedDevicesCount = Array.isArray(
                this.instructionContext['types'][this.mode]['selectedNodes']
              )
                ? this.instructionContext['types'][this.mode]['selectedNodes'].length
                : 0;
            }
          }
          this.validity.emit(this.checkFormValidity());
        });

beforeEach(() => {
    instrcutionServiceSpyApplyInstruction = spyOn(instructionService, 'applyInstruction');
    // !! 删除这一行
    spyOn(instructionService, 'instruction' as any).and.returnValue(of(expectedInstructions));
});