def find_recipe(cookbook, recipe_name = nil)
      recipes = cookbook.recipe_filenames_by_name
      if recipe_name.nil?
        default_recipe = recipes["default"]
        raise NoDefaultRecipe.new(cookbook.root_dir, cookbook.name) if default_recipe.nil?
        default_recipe
      else
        recipe = recipes[recipe_name]
        raise RecipeNotFound.new(cookbook.root_dir, recipe_name, recipes.keys, cookbook.name) if recipe.nil?
        recipe
      end
    end
def find_recipe(cookbook, recipe_name = nil)
      recipes = cookbook.recipe_filenames_by_name
      if recipe_name.nil?
        default_recipe = recipes["default"]
        raise NoDefaultRecipe.new(cookbook.root_dir, cookbook.name) if default_recipe.nil?
        default_recipe
      else
        recipe = recipes[recipe_name]
        raise RecipeNotFound.new(cookbook.root_dir, recipe_name, recipes.keys, cookbook.name) if recipe.nil?
        recipe
      end
    end
Find the specified recipe or default recipe if none is specified.
 Raise an error if recipe cannot be found.