testLoadCssBasic compares expected unoptimized output to itself

common.test, line 883

  $expected = file_get_contents("$path/$file.unoptimized.css");
  $unoptimized_output = drupal_load_stylesheet("$path/$file.unoptimized.css", FALSE);
  $this->assertEqual($unoptimized_output, $expected, t('Unoptimized CSS file has expected contents (@file)', array('@file' => $file)));

The unoptimized output file is loaded both as the expected output and the data passed through drupal_load_stylesheet for testing.
This currently causes the test to pass even with a typo in comment_hacks.css.unoptimized.css that has been fixed in comment_hacks.css, and obviously potential for more important oversights.

I've rolled a first patch that takes care of the differences in comment_hacks.css and css_input_without_import.css, but css_input_with_import.css.unoptimized.css currently only removes the input declarations without substituting the file contents.