diff --git a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
index ece3409c45793e6114ed8eba412da50f1734c554..506a49de8d4f5bb581639324d87493beac708da8 100644
--- a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
+++ b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
@@ -18,8 +18,13 @@ class LinkExternalProtocolsConstraintValidatorTest extends UnitTestCase {
   /**
    * @covers ::validate
    * @dataProvider providerValidate
+   * @runInSeparateProcess
    */
-  public function testValidate($value, $valid) {
+  public function testValidate($url, $valid) {
+    $link = $this->createMock('Drupal\link\LinkItemInterface');
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willReturn(Url::fromUri($url));
     $context = $this->createMock(ExecutionContextInterface::class);
 
     if ($valid) {
@@ -38,7 +43,7 @@ public function testValidate($value, $valid) {
 
     $validator = new LinkExternalProtocolsConstraintValidator();
     $validator->initialize($context);
-    $validator->validate($value, $constraint);
+    $validator->validate($link, $constraint);
   }
 
   /**
@@ -56,15 +61,6 @@ public function providerValidate() {
     // Invalid protocols.
     $data[] = ['ftp://ftp.funet.fi/pub/standards/RFC/rfc959.txt', FALSE];
 
-    foreach ($data as &$single_data) {
-      $url = Url::fromUri($single_data[0]);
-      $link = $this->createMock('Drupal\link\LinkItemInterface');
-      $link->expects($this->any())
-        ->method('getUrl')
-        ->willReturn($url);
-      $single_data[0] = $link;
-    }
-
     return $data;
   }
 
diff --git a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
index 5a67b0483ac67243dd78db387dfd172838f5395e..c4d76e4604f56d86a8d420cc8b7080b3b203b972 100644
--- a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
@@ -449,6 +449,8 @@ public static function providerTestIsExternal() {
    *   Expected escaped value.
    * @param array $protocols
    *   Protocols to allow.
+   *
+   * @runInSeparateProcess
    */
   public function testFilterBadProtocol($uri, $expected, $protocols) {
     UrlHelper::setAllowedProtocols($protocols);
@@ -488,6 +490,8 @@ public static function providerTestFilterBadProtocol() {
    *   Expected escaped value.
    * @param array $protocols
    *   Protocols to allow.
+   *
+   * @runInSeparateProcess
    */
   public function testStripDangerousProtocols($uri, $expected, $protocols) {
     UrlHelper::setAllowedProtocols($protocols);
diff --git a/core/tests/Drupal/Tests/Component/Utility/XssTest.php b/core/tests/Drupal/Tests/Component/Utility/XssTest.php
index 92974486aea42f6852d1996a313ab219a6bec664..9f492f80d8396a20888d516f66ac85f4a03a81c4 100644
--- a/core/tests/Drupal/Tests/Component/Utility/XssTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/XssTest.php
@@ -23,6 +23,8 @@
  * Relevant CVEs:
  * - CVE-2002-1806, ~CVE-2005-0682, ~CVE-2005-2106, CVE-2005-3973,
  *   CVE-2006-1226 (= rev. 1.112?), CVE-2008-0273, CVE-2008-3740.
+ *
+ * @runTestsInSeparateProcesses
  */
 class XssTest extends TestCase {