```ruby
require 'test/unit'


class TestFilter < Test::Unit::TestCase
  # Helpers
  def file_content(file, directory)
    path = File.join('test', directory, file)
    File.new(path).read
  end

  def assert_file(file)
    assert_equal file_content(file, 'expected'), file_content(file, 'filtered')
  end

  # Tests
  def test_empty
    assert_file 'empty.html'
  end

  def test_empty_nodes
    assert_file 'empty_nodes.html'
  end

  def test_strip
    assert_file 'strip.html'
  end

end
```

Test all filtered files at once
user
```ruby
require 'test/unit'


class TestFilter < Test::Unit::TestCase
  # Helpers
  def file_content(file, directory)
    path = File.join('test', directory, file)
    File.new(path).read
  end

  def assert_file(file)
    assert_equal file_content(file, 'expected'), file_content(file, 'filtered')
  end

  # Tests
  def test_filtered
    Dir.glob("test/expected/*.html") do |path|
      assert_file File.basename(path)
    end
  end

end
```
assistant