context "reuse" do
  context "a" do
    reuse_setup do
      $foo ||= 0
      $foo += 1
      @foo = $foo
    end

    should "1 preserve instance state" do
      assert_equal 1, @foo
    end

    should "2 only run setup once" do
      assert_equal 1, $foo
    end

    should "3 preserve instance state" do
      assert_equal 1, @foo
    end

    # nesting does not work!
    # context "nested" do
    #  reuse_setup { ...  }
    # end
  end
end