RxJS - test synchronous subscribve

const { rxObserver } = require('api/v0.3');
const { timer } = require('rxjs');
const { take, map, shareReplay, tap } = require('rxjs/operators');

const source = timer(10, 10)
  .pipe(
    map(time => `${time} deciseconds`),
    take(5),
    tap (x => console.log(x)),
    shareReplay(1)
  );
  
  timer(10, 10).pipe(take(10)).subscribe(() => {
    let message = '0';
    
    source.pipe(take(1)).subscribe(val => {
      message = val
    });
    
    rxObserver(message)
  });