Исходный код Rails определяет это отображение:
"ActionController::RoutingError" => :not_found,
"AbstractController::ActionNotFound" => :not_found,
"ActionController::MethodNotAllowed" => :method_not_allowed,
"ActionController::UnknownHttpMethod" => :method_not_allowed,
"ActionController::NotImplemented" => :not_implemented,
"ActionController::UnknownFormat" => :not_acceptable,
"ActionController::InvalidAuthenticityToken" => :unprocessable_entity,
"ActionController::InvalidCrossOriginRequest" => :unprocessable_entity,
"ActionDispatch::Http::Parameters::ParseError" => :bad_request,
"ActionController::BadRequest" => :bad_request,
"ActionController::ParameterMissing" => :bad_request,
"Rack::QueryParser::ParameterTypeError" => :bad_request,
"Rack::QueryParser::InvalidParameterError" => :bad_request