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

WIP

import { useObservableRef } from '../react/useObservableRef';
import { renderHook } from '@testing-library/react-hooks';
import expect from 'expect';
import { BehaviorSubject, Observable, Subject } from 'rxjs';
describe('useObservableRef', () => {
  it('should allow undefined initial value', () => {
    const subject = new Observable();
    const {
      result: { current: ref },
    } = renderHook(() => useObservableRef(subject));
    expect(ref.current).toBeUndefined();
  });
  it('should allow initial value', () => {
    const subject = new Observable();
    const initial = 'test';
    const {
      result: { current: ref },
    } = renderHook(() => useObservableRef(subject, initial));
    expect(ref.current).toEqual(initial);
  });
  it('should take initial value from a subject', () => {
    const initial = 'test';
    const subject = new BehaviorSubject(initial);
    const {
      result: { current: ref },
    } = renderHook(() => useObservableRef(subject));
    expect(ref.current).toEqual(initial);
  });
  it('should update ref when subject emits', (complete) => {
    const expected = [1, 2];
    const subject = new BehaviorSubject(expected[0]);
    subject.subscribe({ complete });

    const {
      result: { current: ref },
    } = renderHook(() => useObservableRef(subject));

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

    subject.next(expected[0]);
    expect(ref.current).toEqual(expected.shift());
    subject.complete();
  });
  it('should not rerender when subject emits', (complete) => {
    const subject = new Subject();
    let renders = 0;
    const {
      result: { current: ref },
    } = renderHook(() => {
      renders++;
      return useObservableRef(subject);
    });
    expect(renders).toEqual(1);
    Array.from({ length: 9 }, (_, i) => subject.next(++i));
    expect(renders).toEqual(1);
    expect(ref.current).toEqual(9);
    complete();
  });
});