```ruby
require_relative 'helper'
require 'epub/cfi'

class TestCFI < Test::Unit::TestCase
  def test_escape
    assert_equal '^^', EPUB::CFI.escape('^')
  end

  def test_unescape
    assert_equal '^', EPUB::CFI.unescape('^^')
  end
end
```

Add test cases for CFI sorting rules
user
```ruby
require_relative 'helper'
require 'epub/cfi'
require 'epub/parser/cfi'

class TestCFI < Test::Unit::TestCase
  def test_escape
    assert_equal '^^', EPUB::CFI.escape('^')
  end

  def test_unescape
    assert_equal '^', EPUB::CFI.unescape('^^')
  end

  def test_compare
    assert_compare epubcfi('/6/4[id]'), '<', epubcfi('/6/5')
    assert_equal epubcfi('/6/4'), epubcfi('/6/4')
    assert_compare epubcfi('/6/4'), '>', epubcfi('/4/6')
    assert_compare epubcfi('/6/4!/4@3:7'), '>', epubcfi('/6/4!/4')
  end

  private

  def epubcfi(string)
    EPUB::Parser::CFI.new.parse('epubcfi(' + string + ')')
  end
end
```
assistant