test.rb

class Main < Shoes
  url '/', :index
  url '/foo', :foo
  url '/bar', :bar

  def index
    if !owner && !@child #If I am the parent and I have no child
      @child = window(:title => 'child')
    end
    sync_child
    para 'in index'
    button 'go to foo' do
      visit '/foo'
    end
    button 'go to bar' do
      visit '/bar'
    end
  end

  def foo
    sync_child
    para 'in foo'
    button 'go to index' do
      visit '/'
    end
    button 'go to bar' do
      visit '/bar'
    end
  end

  def bar
    sync_child
    para 'in bar'
    button 'go to index' do
      visit '/'
    end
    button 'go to foo' do
      visit '/foo'
    end
  end

  def sync_child
    if !owner && @child
      @child.sync_with_owner!
    end
  end
end

class Shoes::App
  def sync_with_owner!
    visit owner.location
  end
end

Shoes.app(:title => 'parent')