def assert_valid(key, value)
      validators[key].each do |validator|
        validator.call(key, value)
      end
    end
def assert_valid(key, value)
      validators[key].each do |validator|
        validator.call(key, value)
      end
    end
Check if key passes all registered validations for a key

 @param [String] key
 @param [Object] value

 @api private