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

WIP

import { useObservableState } from '../react/useObservableState';
import { renderHook, act } from '@testing-library/react-hooks';
import expect from 'expect';
import { BehaviorSubject, Observable } from 'rxjs';

describe('useObservableState', () => {
  it('should allow undefined initial value', () => {
    const subject = new Observable();
    const {
      result: { current: state },
    } = renderHook(() => useObservableState(subject));
    expect(state).toBeUndefined();
  });
  it('should allow initial value', () => {
    const subject = new Observable();
    const initial = 'test';
    const {
      result: { current: state },
    } = renderHook(() => useObservableState(subject, initial));
    expect(state).toEqual(initial);
  });
  it('should take initial value from a subject', () => {
    const initial = 'test';
    const subject = new BehaviorSubject(initial);
    const {
      result: { current: state },
    } = renderHook(() => useObservableState(subject));
    expect(state).toEqual(initial);
  });
  it('should update state when subject emits', () => {
    const expected = [1, 2, 3, 4, 5];
    const expectedRenderCounts = expected.length;

    const subject = new BehaviorSubject(expected[0]);

    let renderCount = 0;
    const { result } = renderHook(() => {
      renderCount++;
      return useObservableState(subject);
    });

    expect(result.current).toEqual(expected.shift());

    while (expected.length) {
      act(() => subject.next(expected[0]));
      expect(result.current).toEqual(expected.shift());
    }

    expect(renderCount).toBe(expectedRenderCounts);
  });
});