class Hash
  #
  #   require 'facet/hash/assert_has_keys'
  #
  #   h = { :a => 1, :b => 2 }
  #   h.assert_has_keys( :a )   #=> true
  #   h.assert_has_keys( :c )   #=> ArgumentError
  #
  def assert_has_keys(*check_keys)
    raise(ArgumentError, "does not have key(s)") unless has_keys?(*check_keys)
  end
end