Mock a provider class to return response and handle promise - Unit Testing with Jasmine and Karma with Ionic 3

Question

Am a newbie in Unit Testing. I started to write Unit Testing for my Ionic 3 Application using Karma and Jasmine. I followed blogs to get the configurations set and successfully tested the initialisation of App component. I also use ionic-mock to have the mocks.

My first page has a http service call which invokes a provider. Below is the call.

this.portalList.getListInformation().then(data => {
   this.infolist = data;
});

And in provider :

return new Promise((resolve,reject) => {
  this.http.get(url).subscribe(
    data => {
      const response: any = data;
      resolve(response);
    },
    (error) => {
      reject(error);
    })
});

And my .spec.ts is here.

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { By }           from '@angular/platform-browser';
import { DebugElement } from '@angular/core';
import { Portal } from './portal';
import { IonicModule, Platform, NavController, NavParams} from 'ionic-angular/index';
import { StatusBar } from '@ionic-native/status-bar';
import { SplashScreen } from '@ionic-native/splash-screen';
import { PortalList } from '../../providers/PortalList/PortalList';
import { HttpClient, HttpHandler } from '@angular/common/http';

import {
  PlatformMock,
  AppsMock,
  NavParamsMock,
  NavMock,
  PortalListMock
} from '../../../test-config/mocks-ionic';

describe(' Portal Page', () => {
  let de: DebugElement;
  let comp: Portal;
  let fixture: ComponentFixture<Portal>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [Portal],
      imports: [
        IonicModule.forRoot(Portal)
      ],
      providers: [
        Config,HttpClient, HttpHandler
        { provide: App, useClass: AppsMock},
        { provide: Platform, useClass: PlatformMock},
        { provide: NavParams, useClass: NavParamsMock},
        { provide: NavController, useClass: NavMock},
        { provide: PortalList, useClass: PortalListMock}
      ]
    });
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(Portal);
    comp = fixture.componentInstance;
    de = fixture.debugElement.query(By.css('label'));
  });

  it('should create component', () => expect(comp).toBeDefined());

});

I provided the Mock for the provider.

export class PortalListMock {
  public infoList = [{name: "MAC", region: "West"}];

  public _getPortal(): any { return {} };
  public getListInformation() { return this.infoList; }

  return;
}

On executing **npm test**, it gives error like **this.portalList.getListInformation().then is not a function**.

How to mock the promise of the provider http request. or how to overcome from this issue.

Answer 1

I believe this is related to you returning an array, instead of a Promise.

I would suggest the following change in the mock provider:

this:

public getListInformation() { return this.infoList; }

to become this:

public getListInformation() { return Promise.resolve(this.infoList); }

That way you return the resolved promise, which is equivalent to the code inside the real provider:

return new Promise((resolve,reject) => {

but restricted to return the resolved Promise always including the static data.