class Rspec::Core::World

def find(collection, type_of_filter=:positive, conditions={})
  negative = type_of_filter != :positive
  collection.select do |item|
    # negative conditions.any?, positive conditions.all? ?????
    result = conditions.all? do |filter_on, filter| 
      item.metadata.apply_condition(filter_on, filter)
    end
    negative ? !result : result
  end
end