Marble testing with TestScheduler

marble-testing.spec.ts

import { TestScheduler } from "rxjs/testing";
import { Observable } from "rxjs";
import { filter } from "rxjs/operators";

describe("Awesome testing with Marble Diagrams", () => {
  const scheduler = new TestScheduler((actual, expected) => {
    expect(actual).toEqual(expected);
  });

  const isMultipleOfTen = (number: number) => number % 10 === 0;

  it("should filter numbers that aren't multiples of ten", () => {
    scheduler.run(({ cold, expectObservable }) => {
      const values = {
        a: 1, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10
      };
      const number$ = cold("-a-b-c-d-e-f-g-h-i-j|", values);
      const expectedMarbleDiagram = "-------------------a|";
      const expectedValues = { a: 10 };
      const result = number$.pipe(filter(number => isMultipleOfTen(number)));
      expectObservable(result).toBe(expectedMarbleDiagram, expectedValues);
    });
  });
});