Different ways of observables' testing

Let’s assume we have some UserListComponent exposing public stream users$ (typeof User):

type User = {
  id: number;
  name: string;
  email: string;
};

In case we’d like to test it, for this example we’ll need the following setup:

const usersMock: User[] = [
  { id: 1, name: "Johny Bravo", email: "johny.bravo@xoxo.com" },
  { id: 2, name: "React dev", email: "ihatemyjob@really.io" }, // Heey I'm just kidding, Angular 🤝 React
  { id: 3, name: "10x Dev", email: "10xdev@hotmail.com" },
];

const userListComponent = {
  users$: of(usersMock),
};

Then you aren’t limited only to use subscribe() on this Observable, you can pick different ways depending on your case:

it("done func", (done: DoneCallback) => {
  userListComponent.users$.subscribe((expectedUsers: User[]) => {
    expect(expectedUsers).toStrictEqual(usersMock);
    done();
  });
});

it("first value from", async () => {
  const expectedUsers: User[] = await firstValueFrom(userListComponent.users$);
  expect(expectedUsers).toStrictEqual(usersMock);
});

it("Fake async & tick", fakeAsync(() => {
  let expectedUsers;
  userListComponent.users$.subscribe((users: User[]) =>
    setTimeout(() => {
      expectedUsers = users;
    }, 2000)
  );
  tick(2100);
  expect(expectedUsers).toStrictEqual(usersMock);
}));

it("marbles", () => {
  const testScheduler = new TestScheduler((actual, expected) => {
    expect(actual).toStrictEqual(expected);
  });
  testScheduler.run(({ expectObservable }) => {
    expectObservable(userListComponent.users$).toBe("(a|)", {
      a: usersMock,
    });
  });
});