Cause i already needed this information twice and hat troubles researching it every time, i post this here.

Lets pretend we have this methode,

public bool TryGetNext(out Bestellung? bestellung);

what makes it special, it does have a Out Parameter usually if you dont care

It.isAny<Bestellung>()

would be right do declare that this setup is acting on any input as long it is of Type Bestellung

In Case of a Out you need to use It.Ref<Bestellung>.IsAny.

How are we get the setup to give us different results every time we call it?

In my case is the Original Methode a DeQueue so i rebuild this.

.Returns((out Bestellung? bestellung) => {}

here we get the variable bestellung we just assign and with the return as usually assign the return value of the method itself.

Queue<Bestellung> bestellungenQueue = new Queue<Bestellung>(
[
  new BestellungBuilder().WithAuftragsNr(123456).Build(),
  new BestellungBuilder().WithAuftragsNr(789456).Build()
]);

Mock<IBestellungRepository> mockRepository = new Mock<IBestellungRepository>();
mockRepository.Setup(m => m.TryGetNext(out It.Ref<Bestellung>.IsAny!))
    .Returns((out Bestellung? bestellung) =>
    {
      if (bestellungenQueue.Count > 0)
      {
        bestellung = bestellungenQueue.Dequeue();
        return bestellung != null; // Return true if not null
      }

      bestellung = null;
      return false; // No more items
    });