require "abstract_unit" class ParamsWrapperForApiTest < ActionController::TestCase class UsersController < ActionController::API attr_accessor :last_parameters wrap_parameters :person, format: [:json] def test self.last_parameters = params.except(:controller, :action).to_unsafe_h head :ok end end class Person; end tests UsersController def test_specify_wrapper_name @request.env["CONTENT_TYPE"] = "application/json" post :test, params: { "username" => "sikachu" } expected = { "username" => "sikachu", "person" => { "username" => "sikachu" }} assert_equal expected, @controller.last_parameters end end