Mocking localstorage in angular 7

user_4365228 0
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I have used localstorage in my application. based on the comments from my reviewer, Instead of using the localstorage directly, I created a reference of localstorage and used in my application. It works well. but couldn't (I don't know how to) mock the referenced localstorage.

Here's my code:

local-storage-ref.service.ts:

@Injectable()
export class LocalStorageRef {
  public getLocalStorage(): Storage {
    return localStorage;
  }
}

app.component.ts:

import { LocalStorageRef } from './shared/local-storage-ref.service';
...
export class AppComponent implements OnInit {
...
constructor(public ref: LocaStorageRef){
}
...
someFunction(){
...
this.ref.localStorageRef.getLocalStorage().setItem('somekey','sometext');
...
val = this.ref.localStorageRef.getLocalStorage().setItem('somekey');
...
}
}

Spec.ts:

import { LocalStorageRef } from './shared/local-storage-ref.service';
...
describe('#AppComponent', () => {
...
  let mockLocalStorageRef: jasmine.SpyObj<LocalStorageRef>;
...
 beforeEach(async(() => {
...
    mockLocalStorageRef = jasmine.createSpyObj('LocalStorageRef', ['getLocalStorage']);
    mockLocalStorageRef.getLocalStorage.and.callThrough();
...
}
it(){
...
}
}

When i run the test case. I'm getting error like

TypeError: Cannot read property 'getItem' of undefined

I know that I mocked the getLocalStorage() but i don't know how to mock the setItem and getItem which is inside the getLocalStorage(). Any leads would be helpful. Thanks.

karma-jasmine angular unit-testing
2 Answers

Its better to use useClass to create a stub which can reused whenever you are using LocalStorageRef in other components:

LocalStorageRefStub

export class LocalStorageRefStub {

 const mockLocalStorage = {
  getItem: (key: string): string => {
    return key in store ? store[key] : null;
  },
  setItem: (key: string, value: string) => {
    store[key] = `${value}`;
  }
 };
 public getLocalStorage(){
    return mockLocalStorage;
  }

}

and then use it in component.spec.ts as:

  TestBed.configureTestingModule(
   {
     imports: [blahblah],
     providers: [{provide:LocalStorageRef, useClass: LocalStorageRefStub }],
    // and other properties......
   }
   )
user_30923770

Finally, I found the solution on my own. The problem is I'm mocking the getLocalStorage but not the getItem and setItem. So I created two spies and mocked getItem and setItem as given below. and It worked !!!

code:

const mockLocalStorage = {
  getItem: (key: string): string => {
    return key in store ? store[key] : null;
  },
  setItem: (key: string, value: string) => {
    store[key] = `${value}`;
  }
};
...
localStorageRefServiceSpy = jasmine.createSpyObj('LocalStorageRef', ['getLocalStorage']);
getLocalStorageSpy = jasmine.createSpyObj('LocalStorageRef.getLocalStorage', ['getItem', 'setItem']);
localStorageRefServiceSpy.getLocalStorage.and.returnValue(getLocalStorageSpy);
getLocalStorageSpy.getItem.and.callFake(mockLocalStorage.getItem);
getLocalStorageSpy.setItem.and.callFake(mockLocalStorage.setItem);

Hope this helps someone.

user_43652280
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