Testing ngrx meta reducers

Question

I have a meta reducer that should clear the state when logging out.

export function clearState(reducer: ActionReducer<any>): ActionReducer<any> {
  return (state, action) => {
    if (action.type === AuthActionTypes.UNAUTHENTICATED) {
      state = undefined;
    }
    return reducer(state, action);
  };
}

export const metaReducers: MetaReducer<any>[] = [clearState];

I want to unit test this piece of code. I have tested normal reducers before but for me it is hard to apply the same technique when writing a test for the meta reducer. And there are no examples in the docs.

Answer 1

I figured out a way to test it after digging deep in the ngrx source code

const invokeActionReducer = (currentState, action: any) => {
  return clearState((state) => state)(currentState, action);
};

it('should set state to initial value when logout action is dispatched', () => {
  const currentState = { /* state here */ };

  expect(invokeActionReducer(currentState, userUnauthenticated)).toBeFalsy();
});

Source