diff --git a/test/PHPMailer/PHPMailerTest.php b/test/PHPMailer/PHPMailerTest.php
index 40f97387..b35f7993 100644
--- a/test/PHPMailer/PHPMailerTest.php
+++ b/test/PHPMailer/PHPMailerTest.php
@@ -63,62 +63,6 @@ final class PHPMailerTest extends TestCase
         //self::assertTrue($this->mail->send(), $this->mail->ErrorInfo);
     }
 
-    /**
-     * Test injecting a custom validator.
-     */
-    public function testCustomValidator()
-    {
-        //Inject a one-off custom validator
-        self::assertTrue(
-            PHPMailer::validateAddress(
-                'user@example.com',
-                static function ($address) {
-                    return strpos($address, '@') !== false;
-                }
-            ),
-            'Custom validator false negative'
-        );
-        self::assertFalse(
-            PHPMailer::validateAddress(
-                'userexample.com',
-                static function ($address) {
-                    return strpos($address, '@') !== false;
-                }
-            ),
-            'Custom validator false positive'
-        );
-        //Set the default validator to an injected function
-        PHPMailer::$validator = static function ($address) {
-            return 'user@example.com' === $address;
-        };
-        self::assertTrue(
-            $this->Mail->addAddress('user@example.com'),
-            'Custom default validator false negative'
-        );
-        self::assertFalse(
-        //Need to pick a failing value which would pass all other validators
-        //to be sure we're using our custom one
-            $this->Mail->addAddress('bananas@example.com'),
-            'Custom default validator false positive'
-        );
-        //Set validator back to default
-        PHPMailer::$validator = 'php';
-        self::assertFalse(
-        //This is a valid address that FILTER_VALIDATE_EMAIL thinks is invalid
-            $this->Mail->addAddress('first.last@example.123'),
-            'PHP validator not behaving as expected'
-        );
-
-        //Test denying function name callables as validators
-        //See SECURITY.md and CVE-2021-3603
-        //If a `php` function defined in validators.php successfully overrides this built-in validator name,
-        //this would return false – and we don't want to allow that
-        self::assertTrue(PHPMailer::validateAddress('test@example.com', 'php'));
-        //Check that a non-existent validator name falls back to a built-in validator
-        //and does not call a global function with that name
-        self::assertTrue(PHPMailer::validateAddress('test@example.com', 'phpx'));
-    }
-
     /**
      * Word-wrap an ASCII message.
      */
diff --git a/test/PHPMailer/ValidateAddressCustomValidatorTest.php b/test/PHPMailer/ValidateAddressCustomValidatorTest.php
new file mode 100644
index 00000000..bfec3e11
--- /dev/null
+++ b/test/PHPMailer/ValidateAddressCustomValidatorTest.php
@@ -0,0 +1,115 @@
+<?php
+
+/**
+ * PHPMailer - PHP email transport unit tests.
+ * PHP version 5.5.
+ *
+ * @author    Marcus Bointon <phpmailer@synchromedia.co.uk>
+ * @author    Andy Prevost
+ * @copyright 2012 - 2020 Marcus Bointon
+ * @copyright 2004 - 2009 Andy Prevost
+ * @license   http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
+ */
+
+namespace PHPMailer\Test\PHPMailer;
+
+use PHPMailer\PHPMailer\PHPMailer;
+use PHPMailer\Test\TestCase;
+
+/**
+ * Test email address validation using a custom validator.
+ *
+ * @covers \PHPMailer\PHPMailer\PHPMailer::validateAddress
+ */
+final class ValidateAddressCustomValidatorTest extends TestCase
+{
+
+    /**
+     * Test injecting a one-off custom validator.
+     */
+    public function testOneOffCustomValidator()
+    {
+        $callback = static function ($address) {
+            return strpos($address, '@') !== false;
+        };
+
+        self::assertTrue(
+            PHPMailer::validateAddress('user@example.com', $callback),
+            'Custom validator false negative'
+        );
+        self::assertFalse(
+            PHPMailer::validateAddress('userexample.com', $callback),
+            'Custom validator false positive'
+        );
+    }
+
+    /**
+     * Test setting the default validator to an injected function.
+     */
+    public function testSetDefaultValidatorToCustom()
+    {
+        // Set the default validator to an injected function.
+        PHPMailer::$validator = static function ($address) {
+            return 'user@example.com' === $address;
+        };
+
+        self::assertTrue(
+            $this->Mail->addAddress('user@example.com'),
+            'Custom default validator false negative'
+        );
+
+        // Need to pick a failing value which would pass all other validators
+        // to be sure we're using our custom one.
+        self::assertFalse(
+            $this->Mail->addAddress('bananas@example.com'),
+            'Custom default validator false positive'
+        );
+
+        // Set validator back to default
+        PHPMailer::$validator = 'php';
+
+        // This is a valid address that FILTER_VALIDATE_EMAIL thinks is invalid.
+        self::assertFalse(
+            $this->Mail->addAddress('first.last@example.123'),
+            'PHP validator not behaving as expected'
+        );
+    }
+
+    /**
+     * Test denying function name callables as validators.
+     *
+     * See SECURITY.md and CVE-2021-3603.
+     *
+     * @dataProvider dataRejectCallables
+     *
+     * @param string $callback Callback function name.
+     * @param string $message  Message to display if the test would fail.
+     */
+    public function testRejectCallables($callback, $message)
+    {
+        self::assertTrue(PHPMailer::validateAddress('test@example.com', $callback), $message);
+    }
+
+    /**
+     * Data provider.
+     *
+     * @return array
+     */
+    public function dataRejectCallables()
+    {
+        return [
+            // If a `php` function defined in validators.php successfully overrides this built-in validator name,
+            // this would return false - and we don't want to allow that.
+            'php'  => [
+                'callback' => 'php',
+                'message'  => 'Build-in php validator overridden',
+            ],
+            // Check that a non-existent validator name falls back to a built-in validator
+            // and does not call a global function with that name.
+            'phpx' => [
+                'callback' => 'phpx',
+                'message'  => 'Global function called instead of default validator',
+            ],
+        ];
+    }
+}