add comment for credentials test

Author: imeron2433

dev/tests/unit/Magento/FunctionalTestFramework/DataGenerator/Handlers/CredentialStoreTest.php

@@ -13,6 +13,9 @@
 class CredentialStoreTest extends MagentoTestCase
 {
 
+    /**
+     * Test basic encryption/decryption functionality in CredentialStore class.
+     */
     public function testBasicEncryptDecrypt()
     {
         $testKey = 'myKey';