default_url_options in GET form

test.rb

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  # Activate the gem you are reporting the issue against.
  gem "rails", "5.1.0.rc1"
  gem 'minitest-rails-capybara'
end

require "rack/test"
require "action_controller/railtie"

class TestApp < Rails::Application
  config.root = File.dirname(__FILE__)
  config.session_store :cookie_store, key: "cookie_store_key"
  secrets.secret_token    = "secret_token"
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    get "/" => "test#index", as: :root
    get "/foo" => "test#foo"
  end
end

class ApplicationController < ActionController::Base
  def default_url_options(options = {})
    { locale: 'de' }
  end
end

class TestController < ApplicationController
  include Rails.application.routes.url_helpers

  def index
    form = "<h1>Form test</h1>"
    form << "<a href='" + root_path + "'>Root</a>"
    form << "<form action='/foo' method='get'>"
    form << "<input name='bar' value='baz'/>"
    form << "<button id='send' type='submit'>Send</button>"
    form << "</form>"
    render html: form.html_safe
  end

  def foo
    render plain: params
  end
end

require "minitest/autorun"
require 'rails/test_help'
require 'minitest/rails/capybara'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

class BugTest < Minitest::Test
  include Rack::Test::Methods

  feature "Register" do
    scenario "visit link" do
      visit root_path
      click_link 'Root'
      current_url.must_equal 'http://www.example.com/?locale=de'
    end

    scenario "submit form" do
      visit root_path
      click_button 'Send'
      current_url.must_equal 'http://www.example.com/foo?bar=baz&locale=de'
    end
  end

  private
    def app
      Rails.application
    end
end