class DummyStreamWrapper

class DummyStreamWrapper extends LocalStream {
    
    /**
     * {@inheritdoc}
     */
    public function getName() {
        return t('Dummy files');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDescription() {
        return t('Dummy wrapper for simpletest.');
    }
    public function getDirectoryPath() {
        return \Drupal::service('site.path') . '/files';
    }
    
    /**
     * Override getInternalUri().
     *
     * Return a dummy path for testing.
     */
    public function getInternalUri() {
        return '/dummy/example.txt';
    }
    
    /**
     * Override getExternalUrl().
     *
     * Return the HTML URI of a public file.
     */
    public function getExternalUrl() {
        return '/dummy/example.txt';
    }

}