@equinor/fusion-observable/src/__tests__/useObservableEpic.test.ts

WIP

import { renderHook, act } from '@testing-library/react-hooks';
import { filter, map, tap, withLatestFrom } from 'rxjs/operators';
import { useObservableEpic } from '../react';

import { ReactiveObservable } from '../ReactiveObservable';
import type { Epic, Reducer } from '../types';

type State = { value: string; index: number };
type Action = { type: string; payload: string };

describe('useObservableEpic', () => {
  it('should work', (complete) => {
    const initial: State = { value: 'initial', index: 0 };
    const reducer: Reducer<State, Action> = (state, action) => {
      return { value: action.payload, index: state.index + 1 };
    };
    const action1: Action = { type: 'FOO', payload: 'foo' };
    const action2: Action = { type: 'BAR', payload: 'bar' };

    const subject = new ReactiveObservable(reducer, initial);

    /** check that initial state is correct */
    expect(subject.value).toEqual(initial);

    /** assert state when second action is sent to subject */
    subject.addEffect(action2.type, (action, state) => {
      expect(action).toEqual(action2);
      expect(state.index).toBe(2);
      expect(state.value).toEqual(action2.payload);
      /** close subject, end of test */
      subject.complete();
    });

    /** complete test when subject closes */
    subject.subscribe({ complete });

    /** create and epic that triggers when action1 is called */
    const epic$: Epic<Action, State> = (action$, state$) => {
      return action$.pipe(
        filter((x) => x.type === action1.type),
        /** include value from latest state in subject */
        withLatestFrom(state$),
        tap(([action, state]) => {
          expect(action).toEqual(action1);
          expect(state.index).toEqual(1);
          expect(state.value).toEqual(action1.payload);
        }),
        /** return action2 for dispatch in subject */
        map(() => action2),
      );
    };

    /** wire up hook */
    renderHook(() => useObservableEpic(subject, epic$));

    /** trigger subject by dispatching action1 */
    act(() => subject.next(action1));

    /** make sure all assertions are executed */
    expect.assertions(7);
  });
});