```ruby
# frozen_string_literal: true
require_relative '../test_base'
require_code 'utf8_clean'

class Utf8CleanTest < TestBase

  def self.id58_prefix
    '3D9'
  end

  # - - - - - - - - - - - - - - - - -

  test '7FE', %w( cleans invalid encodings ) do
    bad_str = (100..1000).to_a.pack('c*').force_encoding('utf-8')
    refute bad_str.valid_encoding?
    good_str = Utf8.clean(bad_str)
    assert good_str.valid_encoding?
  end

end
```

Add extra assert to utf8.clean() test
user
```ruby
# frozen_string_literal: true
require_relative '../test_base'
require_code 'utf8_clean'

class Utf8CleanTest < TestBase

  def self.id58_prefix
    '3D9'
  end

  # - - - - - - - - - - - - - - - - -

  test '7FE', %w( cleans invalid encodings ) do
    bad_str = (100..1000).to_a.pack('c*').force_encoding('utf-8')
    refute bad_str.valid_encoding?
    good_str = Utf8.clean(bad_str)
    assert good_str.valid_encoding?
    assert good_str.size != bad_str.size
  end

end
```
assistant