How to set the IP address for a test on a Rails app

rails_test_ip_address.rb

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  def index
    render text: "Your IP is #{request.remote_ip}"
  end
end

# test/controllers/users_controller_test.rb
class UsersControllerTest < ActionController::TestCase
  test "should get index" do
    request.env['REMOTE_ADDR'] = '1.2.3.4'
    response = get :index
    assert_equal 'Your IP is 1.2.3.4', response.body
  end
end

request.env['REMOTE_ADDR'] = '1.2.3.4' can be simplified to

self.remote_addr = '127.0.0.1'