Angular2 unit test + creating object of an interface

Question

Little exhausted here, may be that is why my title is not so accurate.

I am writing a unit test for my DummyService:

 import {Injectable} from '@angular/core';

    @Injectable()
    export class DummyService {

        getAllDataSources():Promise<Array<DummyData>> {
            return new Promise<DummyData[]>(resolve =>
                setTimeout(()=>resolve([]), 1000) // 1 seconds
            );
        }
    }

Please assume am returning a list of DummyData objects from getAllDataSources.

Now, I have a structure/interface for the dummy data in the same service file:

 export interface DummyData{
            Name:string;
            IsActive:boolean;
        }

I tried to write unit test for this service:

import {DummyService, DummyData} from './dummy.service';
import {
    beforeEachProviders
} from '@angular/core/testing';

import {provide} from '@angular/core';

export function main() {

    describe('dummy.service', () => {
        let dsService:DummyService;

        it('should fetch data', ()=> {
           dummyData: DummyData = new DummyData(); // >>>> culprit...
           expect(1).toEqual(1);
        });
    });
}

This unit test seem little funny, as I am really not calling DummyServices function to get the list of DummyData.

I am doing this because I was getting some issue, due to which I was not able to see my test. I did some research, spent a whole day and finally found that this structure DummyData is the CULPRIT. I proved this to myself when I tried creating an object of it in my unit test (in the code above) and I got the following error:

FAILED TESTS:
  dummy.service
    ✖ should fetch data
      PhantomJS 2.1.1 (Linux 0.0.0)
      Chrome 50.0.2661 (Linux 0.0.0)
    ReferenceError: **DummyData is not defined**
        at eval (/home/aodev/WebstormProjects/Data Federation App/data-mapping-app/dist/dev/app/shared/datasource.service.spec.js:8:28)
        at Object.eval (/home/aodev/WebstormProjects/Data Federation App/data-mapping-app/node_modules/@angular/core/testing/testing.js:80:25)

So, can someone tell me please, what am I doing wrong? Why I cannot create the object of DummyData inside my unit test?

Please help!

Maybe a missing import for DummyData in your DummyService file. — Günter Zöchbauer
– Günter Zöchbauer, Commented Jun 20, 2016 at 12:04
From the code above, it looks like DummyData is an interface and not a class. Interfaces cannot be instantiated. Because they are not classes. — Estus Flask
– Estus Flask, Commented Jun 20, 2016 at 12:42

kemsky · Accepted Answer · 2016-06-20 14:44:16Z

2

TypeScript interfaces exist only during compile time, runtime knows nothing about interfaces.

This is how you create instance that implements interface:

interface itest
{
    success:boolean;
}

let a:itest = {success: true}; //compiler checks that object matches interface itest

answered Jun 20, 2016 at 14:44

kemsky

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