Validate User Input, Not Developer Input

validate-user-input-not-developer-input.cs

var milkShakeMaker = new MilkShakeMaker();
var shake = milkShakeMaker.MakeShake(icecubes, milk, ingredients);
 
public class MileShakeMaker
{
   public Shake MakeShake(IEnumerable iceCubes,
             IMilk milk, 
             IEnumerable ingredients)
   {
      if(ice == null || milk == null || ingredient == null)
          throw new InvalidArgumentException("You passed in a null, duh");
      if(ice.Count < 1)
          throw new InvalidArgumentException("You need ice.");
      if(milk.IsSpoiled)
          throw new SpoiledMilkException();
      foreach(var ice in iceCubes)
      {
          if(ice.IsMelted())
             throw new MeltedIceException();
      }
 
     if(ingredients.Count < 1)
         throw new InvalidArgumentException("You need some ingredients.");
 
     ...
 
   }
}