CODEWITHSUNDEEP
angularunit-testingjestjsngrx
alex.k
alex.k

Reputation: 183

How do I mock selectors in nrgx 8 unit tests?

I am learning to write unit tests for ngrx8 application using Jest.

I am testing a component that has subscription to a selector in ngOnInit:

ngOnInit(): void {
  this.store.pipe(select(someSelector(this.parameter))).subscribe((res: 
    // some logic here
  });
}

In the .spec.ts file I put provideMockStore in TestBed configuration:

TestBed.configureTestingModule({
    // ...
    providers: [
      provideMockStore({
        initialState, // defined somewhere above
        selectors: [
          {
            selector: someSelector('param'),
            value: {a: 'b', c: 'd'}
          }
        ]
      })
    ]
    // ...
}).compileComponents();;

So I expect that while running this unit test, I should enter the subscription (the "some logic here" section) in the component .ts file and res will equal {a: 'b', c: 'd'}.

That doesn't happen, instead mocked selector is ignored and the real one is used.

Things I tried:

Now I am out of options, and the NGRX documentation doesn't cover almost anything.

Upvotes: 3

Views: 2585

Answers (1)

Wandrille
Wandrille

Reputation: 6821

Mocking the selector doesn't seem to be the best solution. It would be better to mock the store itself.

You can provide the state in : 

provideMockStore({ initialState: your_state })

or

mockStore.setState(your_state);

mockStore.setState(...) allows you to do tests with different value in your store inside your tests.

BUT I suggest you do do the following if you have a complex store:

  • create a class where you will have your mock store state: MockStoreState.

type RecursivePartial<T> = {
  [P in keyof T]?:
  T[P] extends (infer U)[] ? RecursivePartial<U>[] :
    T[P] extends object ? RecursivePartial<T[P]> :
      T[P];
};

export class MockStoreState {
  private store_a: RecursivePartial<Store_A>;
  private store_b: RecursivePartial<Store_b>;

  build(): any {
    const defaultStore_a = {
      ...
    };
    const defaultStore_b = {
      ...
    };

    return {
      store_a: { ...defaultStore_a , ...this.store_a},
      store_b: { ...defaultStore_b , ...this.store_b },
    };
  }

  setStore_a(value: RecursivePartial<Store_A>): Store_A_State {
    this.store_a= value;
    return this;
  }

  setStore_b(value: RecursivePartial<DatasourceState>): Store_B_State {
    this.store_b= value;
    return this;
  }
}
  • Set the state in your store in the test: 
describe(MyComponent.name, () => {
   ...
   let mockStore: MockStore<any>;

   beforeEach(() => {
       ...
       mockStore = TestBed.get(Store);
   })


   it('...', () => {
     const state = new MockStoreState().setStore_a({...})
    .build();

    mockStore.setState(state);

   // HERE you have set the data in your store.
   })
}

Upvotes: 3

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