Only need these validator functions to be loaded for this test

test/PHPMailer/ValidateAddressCustomValidatorTest.php

@@ -87,6 +87,8 @@ final class ValidateAddressCustomValidatorTest extends TestCase
      */
     public function testRejectCallables($callback, $message)
     {
+        require_once \PHPMAILER_INCLUDE_DIR . '/test/validators.php';
+
         self::assertTrue(PHPMailer::validateAddress('test@example.com', $callback), $message);
     }
 

test/TestCase.php

@@ -62,8 +62,6 @@ abstract class TestCase extends PolyfillTestCase
      */
     public static function set_up_before_class()
     {
-        require_once __DIR__ . '/validators.php';
-
         if (defined('PHPMAILER_INCLUDE_DIR') === false) {
             /*
              * Set up default include path.