角度单元测试：如何模拟方法中的属性？

Question

Here is the service that I am trying to test:

@Injectable()
export class BomRevisiosnsService {
    constructor(
        private baseService: BaseService,
        private appConstants: AppConstants,
        private dmConstants: DMConstants
    ) { }

    public getRevisionsData(): any {
        var itemId = this.appConstants.userPreferences.modelData['basicDetails']['itemId'];
        let url = this.dmConstants.URLs.GETBOMREVISIONS + itemId + "/GetRevisionsAsync";
        let headers = {
            "Content-Type": "application/json",
            UserExecutionContext: JSON.stringify(this.appConstants.userPreferences.UserBasicDetails),
        }
        if (itemId != null || itemId != undefined) {
            return this.baseService.getData(url, headers).map(response => {
                return response;
            });
        }
    }
}

spec file

describe('bom-revisions.service ',()=>{
    let bomRevisiosnsService:BomRevisiosnsService;
    let  baseService: BaseService;
    let  appConstants: AppConstants;
    let  dmConstants: DMConstants;
    beforeEach(()=>{
        baseService=new BaseService(null,null);
        appConstants=null;
        dmConstants=null;
        bomRevisiosnsService=new BomRevisiosnsService(baseService,appConstants,dmConstants);
    });
it('getRevisionsData() call base service getData()',()=>{
    let spy = spyOn(baseService, 'getData').and.returnValue(Observable.of())  
    bomRevisiosnsService.getRevisionsData();
    expect(baseService.getData).toHaveBeenCalled();
});

})

Error: TypeError: Cannot read property 'userPreferences' of null

I believe I need to provide some mock value for this.appConstants.userPreferences.modelData['basicDetails']['itemId']; and this.dmConstants.URLs.GETBOMREVISIONS + itemId + "/GetRevisionsAsync";

Answer 1

Yes, indeed, you need to provide a valid value for appConstants and dmConstants because the call to bomRevisiosnsService.getRevisionsData() uses that information internally.

So, instead of assigning null to appConstants and dmConstants , you could create an objects with some valid data, like this:

appConstants = {
  userPreferences: {
    modelData: {
      basicDetails: {
        itemId: 3 // some other valid value here is fine
      }
    },
    UserBasicDetails: {
      // some valid values here, maybe
    }
  }
};

dmConstants = {
  URLs: {
    GETBOMREVISIONS: 'revisions' // or just some valid value according to the use case
  }
};

And the same goes to baseService .

In general, you need to create valid stub, mock, etc for all object, services, etc that are used internally by the service you're testing.