After.cs

private static Gen<Reservation> GenerateReservation =>
  from d in ArbMap.Default.GeneratorFor<DateTime>()
  from e in ArbMap.Default.GeneratorFor<NonWhiteSpaceString>()
  from n in ArbMap.Default.GeneratorFor<NonWhiteSpaceString>()
  from q in ArbMap.Default.GeneratorFor<PositiveInt>()
  select new Reservation
  {
      Date = d,
      Email = e.Item,
      Name = n.Item,
      Quantity = q.Item
  };

Before.cs

private static Gen<Reservation> GenerateReservation =>
  from d in Arb.Default.DateTime().Generator
  from e in Arb.Default.NonWhiteSpaceString().Generator
  from n in Arb.Default.NonWhiteSpaceString().Generator
  from q in Arb.Default.PositiveInt().Generator
  select new Reservation
  {
      Date = d,
      Email = e.Item,
      Name = n.Item,
      Quantity = q.Item
  };