diff --git a/core/modules/editor/src/Tests/QuickEditIntegrationLoadingTest.php b/core/modules/editor/src/Tests/QuickEditIntegrationLoadingTest.php
index 8b8c4bc..0650721 100644
--- a/core/modules/editor/src/Tests/QuickEditIntegrationLoadingTest.php
+++ b/core/modules/editor/src/Tests/QuickEditIntegrationLoadingTest.php
@@ -85,7 +85,7 @@ public function testUsersWithoutPermission() {
       $this->drupalGet('node/1');
 
       // Ensure the text is transformed.
-      $this->assertRaw('<p>Do you also love Drupal?</p><figure class="caption caption-img"><img src="druplicon.png"><figcaption>Druplicon</figcaption></figure>');
+      $this->assertRaw('<p>Do you also love Drupal?</p><figure class="caption caption-img"><img src="druplicon.png" /><figcaption>Druplicon</figcaption></figure>');
 
       // Retrieving the untransformed text should result in an empty 403 response.
       $response = $this->drupalPost('editor/' . 'node/1/body/und/full', 'application/vnd.drupal-ajax', array());
@@ -104,7 +104,7 @@ public function testUserWithPermission() {
     $this->drupalGet('node/1');
 
     // Ensure the text is transformed.
-    $this->assertRaw('<p>Do you also love Drupal?</p><figure class="caption caption-img"><img src="druplicon.png"><figcaption>Druplicon</figcaption></figure>');
+    $this->assertRaw('<p>Do you also love Drupal?</p><figure class="caption caption-img"><img src="druplicon.png" /><figcaption>Druplicon</figcaption></figure>');
 
     $response = $this->drupalPost('editor/' . 'node/1/body/und/full', 'application/vnd.drupal-ajax', array());
     $this->assertResponse(200);
diff --git a/core/modules/filter/src/Tests/FilterHtmlImageSecureTest.php b/core/modules/filter/src/Tests/FilterHtmlImageSecureTest.php
index b7b4fc9..721fa34 100644
--- a/core/modules/filter/src/Tests/FilterHtmlImageSecureTest.php
+++ b/core/modules/filter/src/Tests/FilterHtmlImageSecureTest.php
@@ -124,7 +124,7 @@ function testImageSource() {
       $comment[] = $image . ':';
       // Hash the image source in a custom test attribute, because it might
       // contain characters that confuse XPath.
-      $comment[] = '<img src="' . $image . '" testattribute="' . hash('sha256', $image) . '>';
+      $comment[] = '<img src="' . $image . '" testattribute="' . hash('sha256', $image) . ' />';
     }
     $edit = array(
       'comment_body[0][value]' => implode("\n", $comment),
diff --git a/core/modules/filter/src/Tests/FilterUnitTest.php b/core/modules/filter/src/Tests/FilterUnitTest.php
index f40a03b..cfa132b 100644
--- a/core/modules/filter/src/Tests/FilterUnitTest.php
+++ b/core/modules/filter/src/Tests/FilterUnitTest.php
@@ -51,46 +51,46 @@ function testAlignFilter() {
     };
 
     // No data-align attribute.
-    $input = '<img src="llama.jpg">';
+    $input = '<img src="llama.jpg" />';
     $expected = $input;
     $this->assertIdentical($expected, $test($input)->getProcessedText());
 
     // Data-align attribute: all 3 allowed values.
-    $input = '<img src="llama.jpg" data-align="left">';
-    $expected = '<img src="llama.jpg" class="align-left">';
+    $input = '<img src="llama.jpg" data-align="left" />';
+    $expected = '<img src="llama.jpg" class="align-left" />';
     $this->assertIdentical($expected, $test($input)->getProcessedText());
-    $input = '<img src="llama.jpg" data-align="center">';
-    $expected = '<img src="llama.jpg" class="align-center">';
+    $input = '<img src="llama.jpg" data-align="center" />';
+    $expected = '<img src="llama.jpg" class="align-center" />';
     $this->assertIdentical($expected, $test($input)->getProcessedText());
-    $input = '<img src="llama.jpg" data-align="right">';
-    $expected = '<img src="llama.jpg" class="align-right">';
+    $input = '<img src="llama.jpg" data-align="right" />';
+    $expected = '<img src="llama.jpg" class="align-right" />';
     $this->assertIdentical($expected, $test($input)->getProcessedText());
 
     // Data-align attribute: a disallowed value.
-    $input = '<img src="llama.jpg" data-align="left foobar">';
-    $expected = '<img src="llama.jpg">';
+    $input = '<img src="llama.jpg" data-align="left foobar" />';
+    $expected = '<img src="llama.jpg" />';
     $this->assertIdentical($expected, $test($input)->getProcessedText());
 
     // Empty data-align attribute.
-    $input = '<img src="llama.jpg" data-align="">';
-    $expected = '<img src="llama.jpg">';
+    $input = '<img src="llama.jpg" data-align="" />';
+    $expected = '<img src="llama.jpg" />';
     $this->assertIdentical($expected, $test($input)->getProcessedText());
 
     // Ensure the filter also works with uncommon yet valid attribute quoting.
-    $input = '<img src=llama.jpg data-align=right>';
-    $expected = '<img src="llama.jpg" class="align-right">';
+    $input = '<img src=llama.jpg data-align=right />';
+    $expected = '<img src="llama.jpg" class="align-right" />';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
 
     // Security test: attempt to inject an additional class.
-    $input = '<img src="llama.jpg" data-align="center another-class-here">';
-    $expected = '<img src="llama.jpg">';
+    $input = '<img src="llama.jpg" data-align="center another-class-here" />';
+    $expected = '<img src="llama.jpg" />';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
 
     // Security test: attempt an XSS.
-    $input = '<img src="llama.jpg" data-align="center \'onclick=\'alert(foo);">';
-    $expected = '<img src="llama.jpg">';
+    $input = '<img src="llama.jpg" data-align="center \'onclick=\'alert(foo);" />';
+    $expected = '<img src="llama.jpg" />';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
   }
@@ -117,27 +117,27 @@ function testCaptionFilter() {
     $this->assertIdentical($expected, $test($input)->getProcessedText());
 
     // Data-caption attribute.
-    $input = '<img src="llama.jpg" data-caption="Loquacious llama!">';
-    $expected = '<figure class="caption caption-img"><img src="llama.jpg"><figcaption>Loquacious llama!</figcaption></figure>';
+    $input = '<img src="llama.jpg" data-caption="Loquacious llama!" />';
+    $expected = '<figure class="caption caption-img"><img src="llama.jpg" /><figcaption>Loquacious llama!</figcaption></figure>';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
     $this->assertIdentical($attached_library, $output->getAssets());
 
     // Empty data-caption attribute.
-    $input = '<img src="llama.jpg" data-caption="">';
-    $expected = '<img src="llama.jpg">';
+    $input = '<img src="llama.jpg" data-caption="" />';
+    $expected = '<img src="llama.jpg" />';
     $this->assertIdentical($expected, $test($input)->getProcessedText());
 
     // HTML entities in the caption.
-    $input = '<img src="llama.jpg" data-caption="&ldquo;Loquacious llama!&rdquo;">';
-    $expected = '<figure class="caption caption-img"><img src="llama.jpg"><figcaption>“Loquacious llama!”</figcaption></figure>';
+    $input = '<img src="llama.jpg" data-caption="&ldquo;Loquacious llama!&rdquo;" />';
+    $expected = '<figure class="caption caption-img"><img src="llama.jpg" /><figcaption>“Loquacious llama!”</figcaption></figure>';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
     $this->assertIdentical($attached_library, $output->getAssets());
 
     // HTML encoded as HTML entities in data-caption attribute.
-    $input = '<img src="llama.jpg" data-caption="&lt;em&gt;Loquacious llama!&lt;/em&gt;">';
-    $expected = '<figure class="caption caption-img"><img src="llama.jpg"><figcaption><em>Loquacious llama!</em></figcaption></figure>';
+    $input = '<img src="llama.jpg" data-caption="&lt;em&gt;Loquacious llama!&lt;/em&gt;" />';
+    $expected = '<figure class="caption caption-img"><img src="llama.jpg" /><figcaption><em>Loquacious llama!</em></figcaption></figure>';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
     $this->assertIdentical($attached_library, $output->getAssets());
@@ -145,28 +145,28 @@ function testCaptionFilter() {
     // HTML (not encoded as HTML entities) in data-caption attribute, which is
     // not allowed by the HTML spec, but may happen when people manually write
     // HTML, so we explicitly support it.
-    $input = '<img src="llama.jpg" data-caption="<em>Loquacious llama!</em>">';
-    $expected = '<figure class="caption caption-img"><img src="llama.jpg"><figcaption><em>Loquacious llama!</em></figcaption></figure>';
+    $input = '<img src="llama.jpg" data-caption="<em>Loquacious llama!</em>" />';
+    $expected = '<figure class="caption caption-img"><img src="llama.jpg" /><figcaption><em>Loquacious llama!</em></figcaption></figure>';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
     $this->assertIdentical($attached_library, $output->getAssets());
 
     // Security test: attempt an XSS.
-    $input = '<img src="llama.jpg" data-caption="<script>alert(\'Loquacious llama!\')</script>">';
-    $expected = '<figure class="caption caption-img"><img src="llama.jpg"><figcaption>alert(\'Loquacious llama!\')</figcaption></figure>';
+    $input = '<img src="llama.jpg" data-caption="<script>alert(\'Loquacious llama!\')</script>" />';
+    $expected = '<figure class="caption caption-img"><img src="llama.jpg" /><figcaption>alert(\'Loquacious llama!\')</figcaption></figure>';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
     $this->assertIdentical($attached_library, $output->getAssets());
 
     // Ensure the filter also works with uncommon yet valid attribute quoting.
-    $input = '<img src=llama.jpg data-caption=\'Loquacious llama!\'>';
-    $expected = '<figure class="caption caption-img"><img src="llama.jpg"><figcaption>Loquacious llama!</figcaption></figure>';
+    $input = '<img src=llama.jpg data-caption=\'Loquacious llama!\' />';
+    $expected = '<figure class="caption caption-img"><img src="llama.jpg" /><figcaption>Loquacious llama!</figcaption></figure>';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
     $this->assertIdentical($attached_library, $output->getAssets());
 
     // Finally, ensure that this also works on any other tag.
-    $input = '<video src="llama.jpg" data-caption="Loquacious llama!">';
+    $input = '<video src="llama.jpg" data-caption="Loquacious llama!" />';
     $expected = '<figure class="caption caption-video"><video src="llama.jpg"></video><figcaption>Loquacious llama!</figcaption></figure>';
     $output = $test($input);
     $this->assertIdentical($expected, $output->getProcessedText());
@@ -236,7 +236,7 @@ function testLineBreakFilter() {
       // Single line breaks should be changed to <br> tags, while paragraphs
       // separated with double line breaks should be enclosed with <p></p> tags.
       "aaa\nbbb\n\nccc" => array(
-        "<p>aaa<br>\nbbb</p>\n<p>ccc</p>" => TRUE,
+        "<p>aaa<br />\nbbb</p>\n<p>ccc</p>" => TRUE,
       ),
       // Skip contents of certain block tags entirely.
       "<script>aaa\nbbb\n\nccc</script>
@@ -268,7 +268,7 @@ function testLineBreakFilter() {
       ),
       "<pre>aaa\nbbb\nccc</pre>\nddd\neee" => array(
         "<pre>aaa\nbbb\nccc</pre>" => TRUE,
-        "<p>ddd<br>\neee</p>" => TRUE,
+        "<p>ddd<br />\neee</p>" => TRUE,
       ),
       // Comments remain unchanged and subsequent lines/paragraphs are
       // transformed normally.
@@ -824,8 +824,8 @@ function testHtmlCorrectorFilter() {
     $this->assertEqual($f, '<div id="d">content</div>', 'HTML corrector -- unclosed tag with attribute.');
 
     // XHTML slash for empty elements.
-    $f = Html::normalize('<hr><br>');
-    $this->assertEqual($f, '<hr /><br>', 'HTML corrector -- XHTML closing slash.');
+    $f = Html::normalize('<hr /><br />');
+    $this->assertEqual($f, '<hr /><br />', 'HTML corrector -- XHTML closing slash.');
 
     $f = Html::normalize('<P>test</P>');
     $this->assertEqual($f, '<p>test</p>', 'HTML corrector -- Convert uppercased tags to proper lowercased ones.');
@@ -833,38 +833,38 @@ function testHtmlCorrectorFilter() {
     $f = Html::normalize('<P>test</p>');
     $this->assertEqual($f, '<p>test</p>', 'HTML corrector -- Convert uppercased tags to proper lowercased ones.');
 
-    $f = Html::normalize('test<hr>');
-    $this->assertEqual($f, 'test<hr>', 'HTML corrector -- Let proper XHTML pass through.');
+    $f = Html::normalize('test<hr />');
+    $this->assertEqual($f, 'test<hr />', 'HTML corrector -- Let proper XHTML pass through.');
 
-    $f = Html::normalize('test<hr>');
-    $this->assertEqual($f, 'test<hr>', 'HTML corrector -- Let proper XHTML pass through, but ensure there is a single space before the closing slash.');
+    $f = Html::normalize('test<hr/>');
+    $this->assertEqual($f, 'test<hr />', 'HTML corrector -- Let proper XHTML pass through, but ensure there is a single space before the closing slash.');
 
-    $f = Html::normalize('test<hr >');
-    $this->assertEqual($f, 'test<hr>', 'HTML corrector -- Let proper XHTML pass through, but ensure there are not too many spaces before the closing slash.');
+    $f = Html::normalize('test<hr   />');
+    $this->assertEqual($f, 'test<hr />', 'HTML corrector -- Let proper XHTML pass through, but ensure there are not too many spaces before the closing slash.');
 
     $f = Html::normalize('<span class="test" />');
     $this->assertEqual($f, '<span class="test"></span>', 'HTML corrector -- Convert XHTML that is properly formed but that would not be compatible with typical HTML user agents.');
 
-    $f = Html::normalize('test1<br class="test">test2');
-    $this->assertEqual($f, 'test1<br class="test">test2', 'HTML corrector -- Automatically close single tags.');
+    $f = Html::normalize('test1<br class="test" />test2');
+    $this->assertEqual($f, 'test1<br class="test" />test2', 'HTML corrector -- Automatically close single tags.');
 
     $f = Html::normalize('line1<hr>line2');
-    $this->assertEqual($f, 'line1<hr>line2', 'HTML corrector -- Automatically close single tags.');
+    $this->assertEqual($f, 'line1<hr />line2', 'HTML corrector -- Automatically close single tags.');
 
     $f = Html::normalize('line1<HR>line2');
-    $this->assertEqual($f, 'line1<hr>line2', 'HTML corrector -- Automatically close single tags.');
+    $this->assertEqual($f, 'line1<hr />line2', 'HTML corrector -- Automatically close single tags.');
 
     $f = Html::normalize('<img src="http://example.com/test.jpg">test</img>');
-    $this->assertEqual($f, '<img src="http://example.com/test.jpg">test', 'HTML corrector -- Automatically close single tags.');
+    $this->assertEqual($f, '<img src="http://example.com/test.jpg" />test', 'HTML corrector -- Automatically close single tags.');
 
     $f = Html::normalize('<br></br>');
-    $this->assertEqual($f, '<br>', "HTML corrector -- Transform empty tags to a single closed tag if the tag's content model is EMPTY.");
+    $this->assertEqual($f, '<br />', "HTML corrector -- Transform empty tags to a single closed tag if the tag's content model is EMPTY.");
 
     $f = Html::normalize('<div></div>');
     $this->assertEqual($f, '<div></div>', "HTML corrector -- Do not transform empty tags to a single closed tag if the tag's content model is not EMPTY.");
 
-    $f = Html::normalize('<p>line1<br><hr>line2</p>');
-    $this->assertEqual($f, '<p>line1<br></p><hr>line2', 'HTML corrector -- Move non-inline elements outside of inline containers.');
+    $f = Html::normalize('<p>line1<br /><hr />line2</p>');
+    $this->assertEqual($f, '<p>line1<br /></p><hr />line2', 'HTML corrector -- Move non-inline elements outside of inline containers.');
 
     $f = Html::normalize('<p>line1<div>line2</div></p>');
     $this->assertEqual($f, '<p>line1</p><div>line2</div>', 'HTML corrector -- Move non-inline elements outside of inline containers.');
@@ -872,8 +872,8 @@ function testHtmlCorrectorFilter() {
     $f = Html::normalize('<p>test<p>test</p>\n');
     $this->assertEqual($f, '<p>test</p><p>test</p>\n', 'HTML corrector -- Auto-close improperly nested tags.');
 
-    $f = Html::normalize('<p>Line1<br><STRONG>bold stuff</b>');
-    $this->assertEqual($f, '<p>Line1<br><strong>bold stuff</strong></p>', 'HTML corrector -- Properly close unclosed tags, and remove useless closing tags.');
+    $f = Html::normalize('<p>Line1<br /><STRONG>bold stuff</b>');
+    $this->assertEqual($f, '<p>Line1<br /><strong>bold stuff</strong></p>', 'HTML corrector -- Properly close unclosed tags, and remove useless closing tags.');
 
     $f = Html::normalize('test <!-- this is a comment -->');
     $this->assertEqual($f, 'test <!-- this is a comment -->', 'HTML corrector -- Do not touch HTML comments.');
diff --git a/core/modules/system/src/Tests/Common/AddFeedTest.php b/core/modules/system/src/Tests/Common/AddFeedTest.php
index 9e35a57..8de6090 100644
--- a/core/modules/system/src/Tests/Common/AddFeedTest.php
+++ b/core/modules/system/src/Tests/Common/AddFeedTest.php
@@ -79,7 +79,7 @@ function testBasicFeedAddNoTitle() {
   function urlToRSSLinkPattern($url, $title = '') {
     // Escape any regular expression characters in the URL ('?' is the worst).
     $url = preg_replace('/([+?.*])/', '[$0]', $url);
-    $generated_pattern = '%<link +title="' . $title . '" +type="application/rss.xml" +href="' . $url . '" +rel="alternate" *>%';
+    $generated_pattern = '%<link +title="' . $title . '" +type="application/rss.xml" +href="' . $url . '" +rel="alternate" */>%';
     return $generated_pattern;
   }
 
diff --git a/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php b/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php
index f828eed..d319de3 100644
--- a/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php
+++ b/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php
@@ -73,7 +73,7 @@ function testRenderFile() {
     $this->assertTrue(strpos($styles, $css) > 0, 'Rendered CSS includes the added stylesheet.');
     // Verify that newlines are properly added inside style tags.
     $query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
-    $css_processed = '<link rel="stylesheet" href="' . String::checkPlain(file_create_url($css)) . "?" . $query_string . '" media="all">';
+    $css_processed = '<link rel="stylesheet" href="' . String::checkPlain(file_create_url($css)) . "?" . $query_string . '" media="all" />';
     $this->assertEqual(trim($styles), $css_processed, 'Rendered CSS includes newlines inside style tags for JavaScript use.');
   }
 
diff --git a/core/modules/system/src/Tests/Common/RenderElementTypesTest.php b/core/modules/system/src/Tests/Common/RenderElementTypesTest.php
index ebd4300..8d53fe4 100644
--- a/core/modules/system/src/Tests/Common/RenderElementTypesTest.php
+++ b/core/modules/system/src/Tests/Common/RenderElementTypesTest.php
@@ -91,7 +91,7 @@ function testHtmlTag() {
         'name' => 'description',
         'content' => 'Drupal test',
       ),
-    ), '<meta name="description" content="Drupal test">' . "\n", "#type 'html_tag' auto-closure meta tag generation");
+    ), '<meta name="description" content="Drupal test" />' . "\n", "#type 'html_tag' auto-closure meta tag generation");
 
     // Test title tag generation.
     $this->assertElements(array(
diff --git a/core/modules/system/src/Tests/System/AdminMetaTagTest.php b/core/modules/system/src/Tests/System/AdminMetaTagTest.php
index c7b4ff8..e97d591 100644
--- a/core/modules/system/src/Tests/System/AdminMetaTagTest.php
+++ b/core/modules/system/src/Tests/System/AdminMetaTagTest.php
@@ -20,7 +20,7 @@ class AdminMetaTagTest extends WebTestBase {
    */
   public function testMetaTag() {
     list($version, ) = explode('.', \Drupal::VERSION);
-    $string = '<meta name="Generator" content="Drupal ' . $version . ' (http://drupal.org)">';
+    $string = '<meta name="Generator" content="Drupal ' . $version . ' (http://drupal.org)" />';
     $this->drupalGet('node');
     $this->assertRaw($string, 'Fingerprinting meta tag generated correctly.', 'System');
   }
diff --git a/core/modules/system/src/Tests/System/DefaultMobileMetaTagsTest.php b/core/modules/system/src/Tests/System/DefaultMobileMetaTagsTest.php
index bbda97e..28228b0 100644
--- a/core/modules/system/src/Tests/System/DefaultMobileMetaTagsTest.php
+++ b/core/modules/system/src/Tests/System/DefaultMobileMetaTagsTest.php
@@ -19,7 +19,7 @@ class DefaultMobileMetaTagsTest extends WebTestBase {
   protected function setUp() {
     parent::setUp();
     $this->default_metatags = array(
-      'viewport' => '<meta name="viewport" content="width=device-width, initial-scale=1.0">',
+      'viewport' => '<meta name="viewport" content="width=device-width, initial-scale=1.0" />',
     );
   }