Roderik Muit
--- a/tests/src/Functional/CustomElementsRenderMarkupTest.php
+++ b/tests/src/Functional/CustomElementsRenderMarkupTest.php
+   *   reordered, explicit closing tag == self-closing tag, ...). As of PHP8.1,
+   *   some PHPunit configurations do not report the actual XML comparison
+   *   error. Pass TRUE:
+   *   - if the format of the XML (e.g. the way a tag is closed) matters;
+   *   - if the markup isn't valid XML;
+   *   - (temporarily?) if it's not clear why a test is failing.
+   */
+  protected function assertXmlEquals($expected_markup, $tested_markup, $compare_as_text = FALSE) {
+    if ($compare_as_text) {
+      Assert::assertEquals($this->trim($expected_markup), $this->trim($tested_markup));
+    }
+    else {
+      Assert::assertXmlStringEqualsXmlString($this->trim($expected_markup), $this->trim($tested_markup));
+    }
+  }
+
--- a/tests/src/Functional/CustomElementsRenderMarkupTest.php
+++ b/tests/src/Functional/CustomElementsRenderMarkupTest.php
        'format' => 'restricted_html',
      ],
    ]);
-    $this->node->field_paragraphs = [
-      0 => ['entity' => $paragraph],
-    ];
--- a/tests/src/Functional/CustomElementsRenderMarkupTest.php
+++ b/tests/src/Functional/CustomElementsRenderMarkupTest.php
    $custom_element = $this->getCustomElementGenerator()
      ->generate($paragraph, 'full');
    $markup = $this->renderCustomElement($custom_element);
-    $expected_markup = <<<EOF
-<pg-link href="http://example.com" title="Example site" type="link" view-mode="full"/>
-EOF;
-    Assert::assertXmlStringEqualsXmlString($this->trim($expected_markup), $this->trim($markup));
+    if (!$expected_markup) {
+      $expected_markup = <<<EOF
+  <pg-link href="http://example.com" title="Example site" type="link" view-mode="full"/>
+  EOF;
+    }
+    $this->assertXmlEquals($expected_markup, $markup);