only in patch2:
unchanged:
--- a/src/Tests/RelToAbsTest.php
+++ b/src/Tests/RelToAbsTest.php
@@ -41,8 +41,8 @@ class RelToAbsTest extends WebTestBase {
 
     $filter = new \Drupal\rel_to_abs\Plugin\Filter\RelToAbs(array(), 'rel_to_abs', array('provider' => 'rel_to_abs'));
 
-    $markup = '<div><a href="/node/1">link</a><img src="/files/test.jpg"/><span background="/files/test.jpg">test</span></div>';
-    $check = '<div><a href="' . $front . '/node/1">link</a><img src="' . $front . '/files/test.jpg"/><span background="' . $front . '/files/test.jpg">test</span></div>';
+    $markup = '<div><a href="/node/1">link</a><img src="/files/test.jpg"/><span background="/files/test.jpg">test</span><a href="mailto:test@test.test"></a><a href="#anchor"></a></div>';
+    $check = '<div><a href="' . $front . '/node/1">link</a><img src="' . $front . '/files/test.jpg"/><span background="' . $front . '/files/test.jpg">test</span><a href="mailto:test@test.test"></a><a href="#anchor"></a></div>';
 
     $result = $filter->process($markup, NULL);