D8 Upload file with managed_file or file

Hi all,

Please, Someone can help me with the best way to upload and rename my file with managed_file field.

I tried this code, everything is good but my files are temporary:

BuildForm

       $form['test_field'] = array(
            '#title' => 'Join file',
            '#type' => 'file',
        );

        $form['valider'] = array(
            '#type' => 'submit',
            '#value' => t('Save'),
        );

        return $form;

ValidateForm

public function validateForm(array &$form, FormStateInterface $form_state) {
        $validators = array(
            'file_validate_size' => array(2 * 1024 * 1024), // 2MB file size limit
        );

        $file = file_save_upload('test_field', $validators, 'public://my_folder', FILE_EXISTS_RENAME);

        if ($file== NULL) {
            $form_state->setErrorByName('test_field', 'Error');
            return;
        }
        $parts = pathinfo($file->getFileUri());

        $form_state->setValue('test_field', $parts[basename]);

        if (null !== $file) {
            $file->save();
            $file= reset($file);
        }
    }