Assert the list of modules are enabled or disabled.
$modules: Module list to check.
$enabled: Expected module state.
function assertModules(array $modules, $enabled) {
  system_list_reset();
  foreach ($modules as $module) {
    if ($enabled) {
      $message = 'Module "@module" is enabled.';
    }
    else {
      $message = 'Module "@module" is not enabled.';
    }
    $this
      ->assertEqual(module_exists($module), $enabled, format_string($message, array(
      '@module' => $module,
    )));
  }
}