404 status in functional test

routes.rb

UsersRailsWeb::Application.routes.draw do

  match 'users/show', :controller => 'users', :action => 'show'

end

users_controller.rb

class UsersController < ApplicationController
  before_filter :params_json

  def show
    @users = User.all

   respond_to do |format|
     format.json { render :json => @users }
   end
  end

  protected
    def params_json
      render :json => { :errors => "404" }, :status => 404 unless params[:format] == "json"
    end

end

users_controller_test.rb

require 'test_helper'

class UsersControllerTest < ActionController::TestCase

  test "Get users" do
    # /users/show.json

    get 'show', {:format => :json}

    body = JSON.parse(response.body)

    assert_equal "foo", body[0]["name"]
  end
end