observables_assert_testing.js

import { of } from 'rxjs';
import { map, toArray, mergeMap, delay, catchError } from 'rxjs/operators';

describe('subscribe & assert testing in RxJS', () => {
  it('should compare each emitted value', () => {
    const source$ = of(1,2,3)
    const final$ = source$.pipe(map(value => value * 10))
    // array with expected values
    const expected = [10, 20, 30]
    // we'll use the index and increment it after each call
    let index = 0;
   
    final$.subscribe(value => {
      expect(value).toEqual(expected[index])
      index++
    })
  })

  it('should compare each emitted value with toArray', () => {
    const source$ = of(1,2,3)
    const final$ = source$.pipe(
      map(value => value * 10),
      toArray()
    )
    // array with expected values
    const expected = [10, 20, 30]

    final$.subscribe(value => {
      expect(value).toEqual(expected)
    })
  }) 

  //Use a single argument called done. Jest will wait until the done callback is called before finishing the test.
  it('should let you test async operations with done callback', done => {
    const source$ = of('Ready','Set', 'Go').pipe(
      // delay each emission so we have async behavior
      mergeMap((message, index) => of(message).pipe(delay(index * 1000)))
    );
    const expected = ['Ready', 'Set', 'Go'];
    let index = 0

    source$.subscribe(value => {
      expect(value).toEqual(expected[index])
      index++
      // Run done() on complete
    }, null, done)
  }) 

    //Use a single argument called done. Jest will wait until the done callback is called before finishing the test.
  it('should let you test errors and error messages', () => {
    const source$ = of({first: 'Brian', last: 'Smith'}, null).pipe(
      // delay each emission so we have async behavior
      map(o => `${o.first} ${o.last}`),
      catchError(() => {
        throw 'Invalid response!'
      })
    );

    const expected = ['Brian Smith', 'Invalid response!'];
    const actual = []

    source$.subscribe({
      next: value => {
        actual.push(value)
      },
      error: error => {
        actual.push(error)
        expect(actual).toEqual(expected)
      }
    })
  }) 
})