Overrides \Drupal\system\Tests\Upgrade\UpgradePathTestBase::setUp().
Overrides BareMinimalUpgradePathTest::setUp
public function setUp() {
  parent::setUp();
  // Override $conf_path and $config_directories in settings.php.
  $settings['conf_path'] = (object) array(
    'value' => $this->public_files_directory,
    'required' => TRUE,
  );
  $settings['config_directories'] = (object) array(
    'value' => array(),
    'required' => TRUE,
  );
  $this
    ->writeSettings($settings);
}