testMenuTreeData() assert message confuses dashes and underscores

The assert messages in testMenuTreeData() mention that "hyphens are changed to dashes", but hyphens and dashes are the same thing. It should be "changed to underscores".

    // Validate that the - in main-menu is changed into an underscore
    $this->assertEqual($output['1']['#theme'], 'menu_link__main_menu', 'Hyphen is changed to a dash on menu_link');
    $this->assertEqual($output['#theme_wrappers'][0], 'menu_tree__main_menu', 'Hyphen is changed to a dash on menu_tree wrapper');

This also occurs in D7.