acquia_commercemanager-8.x-1.122/modules/acm_payment/acm_payment.module

<?php

/**
 * @file
 * Contains acm_payment.module.
 */

/**
 * Implements hook_theme().
 */
function acm_payment_theme($existing, $type, $theme, $path) {
  return [
    'acm_payment' => [
      'render element' => 'form',
      'variables' => [
        'payment_method' => '',
        'payment_method_name' => '',
      ],
    ],
    'acm_payment__braintree' => [
      'base hook' => 'acm_payment',
    ],
  ];
}

/**
 * Implements hook_theme_suggestions_HOOK().
 */
function acm_payment_theme_suggestions_acm_payment(array $variables) {
  $suggestions = [];
  $paymentMethod = $variables['payment_method'];
  $suggestions[] = 'acm_payment__' . $paymentMethod;
  return $suggestions;
}