diff -u b/core/modules/link/tests/src/Functional/LinkFieldTest.php b/core/modules/link/tests/src/Functional/LinkFieldTest.php
--- b/core/modules/link/tests/src/Functional/LinkFieldTest.php
+++ b/core/modules/link/tests/src/Functional/LinkFieldTest.php
@@ -163,9 +163,9 @@
     $validation_error_2 = 'Manually entered paths should start with one of the following characters: / ? #';
     $validation_error_3 = "The path '@link_path' is inaccessible.";
     $invalid_external_entries = [
-      // Invalid protocol
+      // Invalid protocol.
       'invalid://not-a-valid-protocol' => $validation_error_1,
-      // Missing host name
+      // Missing host name.
       'http://' => $validation_error_1,
     ];
     $invalid_internal_entries = [
@@ -220,7 +220,7 @@
       $this->drupalGet('entity_test/add');
       $this->submitForm($edit, 'Save');
       preg_match('|entity_test/manage/(\d+)|', $this->getUrl(), $match);
-      $id = $match[1];
+      $id = !empty($match) ? $match[1] : '';
       $this->assertSession()->pageTextContains('entity_test ' . $id . ' has been created.');
       $this->assertRaw('"' . $string . '"');
     }
@@ -416,7 +416,8 @@
     $this->drupalGet('entity_test/add');
     $url1 = 'http://www.example.com/content/articles/archive?author=John&year=2012#com';
     $url2 = 'http://www.example.org/content/articles/archive?author=John&year=2012#org';
-    $url3 = '#net';
+    // The (#tag) fragment is tested within testURLValidation().
+    $url3 = '/#tag';
     $title1 = $url1;
     // Intentionally contains an ampersand that needs sanitization on output.
     $title2 = 'A very long & strange example title that could break the nice layout of the site';
@@ -434,7 +435,7 @@
     $this->assertSession()->pageTextContains('Read more about this entity');
     $this->submitForm($edit, 'Save');
     preg_match('|entity_test/manage/(\d+)|', $this->getUrl(), $match);
-    $id = $match[1];
+    $id = !empty($match) ? $match[1] : '';
     $this->assertSession()->pageTextContains('entity_test ' . $id . ' has been created.');
 
     // Verify that the link is output according to the formatter settings.
@@ -453,6 +454,7 @@
         ['url_only' => TRUE, 'url_plain' => TRUE],
       ],
     ];
+    $url3 = Url::fromUserInput($url3, [])->toString();
     foreach ($options as $setting => $values) {
       foreach ($values as $new_value) {
         // Update the field formatter settings.
@@ -572,7 +574,7 @@
     $this->drupalGet('entity_test/add');
     $url1 = 'http://www.example.com/content/articles/archive?author=John&year=2012#com';
     $url2 = 'http://www.example.org/content/articles/archive?author=John&year=2012#org';
-    $url3 = '#net';
+    $url3 = '/#net';
     // Intentionally contains an ampersand that needs sanitization on output.
     $title2 = 'A very long & strange example title that could break the nice layout of the site';
     $title3 = 'Fragment only';
@@ -585,7 +587,7 @@
     ];
     $this->submitForm($edit, 'Save');
     preg_match('|entity_test/manage/(\d+)|', $this->getUrl(), $match);
-    $id = $match[1];
+    $id = !empty($match) ? $match[1] : '';
     $this->assertSession()->pageTextContains('entity_test ' . $id . ' has been created.');
 
     // Verify that the link is output according to the formatter settings.
@@ -594,6 +596,7 @@
       'rel' => [NULL, 'nofollow'],
       'target' => [NULL, '_blank'],
     ];
+    $url3 = Url::fromUserInput($url3, [])->toString();
     foreach ($options as $setting => $values) {
       foreach ($values as $new_value) {
         // Update the field formatter settings.
@@ -803,7 +806,7 @@
     $this->drupalGet('/entity_test/add');
     $this->submitForm($edit, 'Save');
     preg_match('|entity_test/manage/(\d+)|', $this->getUrl(), $match);
-    $id = $match[1];
+    $id = !empty($match) ? $match[1] : '';
     $output = $this->renderTestEntity($id);
     $expected_link = (string) $this->container->get('link_generator')->generate('Title, no link', Url::fromUri('route:<nolink>'));
     $this->assertStringContainsString($expected_link, $output);
diff -u b/core/modules/link/tests/src/Kernel/LinkItemUrlValidationTest.php b/core/modules/link/tests/src/Kernel/LinkItemUrlValidationTest.php
--- b/core/modules/link/tests/src/Kernel/LinkItemUrlValidationTest.php
+++ b/core/modules/link/tests/src/Kernel/LinkItemUrlValidationTest.php
@@ -91,7 +91,7 @@
       ["http://foo.com/blah_(wikipedia)#cite-1", []],
       ["http://foo.com/blah_(wikipedia)_blah#cite-1", []],
       // The following invalid URLs produce false positives.
-      ["http://foo.com/unicode_(✪)_in_parens", [$violation_2]],
+      ["http://foo.com/unicode_(✪)_in_parens", [$violation_2]],
       ["http://foo.com/(something)?after=parens", []],
       ["http://☺.damowmow.com/", []],
       ["http://code.google.com/events/#&product=browser", []],
@@ -103,7 +103,7 @@
       ["http://-.~_!$&'()*+,;=:%40:80%2f::::::@example.com", [$violation_2]],
       ["http://1337.net", []],
       ["http://a.b-c.de", []],
-      ["rdar://1234", [$violation_0]],
+      ["radar://1234", [$violation_0]],
       ["h://test", [$violation_0]],
       ["ftps://foo.bar/", [$violation_0]],
       // Use invalid URLS from