tests/src/Kernel/EntityEmbedFilterTest.php     | 31 +++++---------------------
 tests/src/Kernel/EntityEmbedFilterTestBase.php | 16 ++++++++++++-
 2 files changed, 21 insertions(+), 26 deletions(-)

diff --git a/tests/src/Kernel/EntityEmbedFilterTest.php b/tests/src/Kernel/EntityEmbedFilterTest.php
index f841858..d584ecd 100644
--- a/tests/src/Kernel/EntityEmbedFilterTest.php
+++ b/tests/src/Kernel/EntityEmbedFilterTest.php
@@ -83,7 +83,7 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
       return;
     }
     $this->assertNotContains('drupal-entity data-entity-type="node" data-entity', $output);
-    $this->assertNotContains('This placeholder should not be rendered.', $output);
+    $this->assertEntityEmbedFilterHasRun($output);
 
     $this->assertContainsMultiple($contains, $output);
     $this->assertNotContainsMultiple($not_contains, $output);
@@ -285,6 +285,7 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
     /** @var \Drupal\filter\FilterProcessResult $filter_result */
     $filter_result = $this->filter->process($content, 'en');
     $output = $filter_result->getProcessedText();
+    $this->assertEntityEmbedFilterHasRun($output);
 
     $this->assertContainsMultiple($contains, $output);
     $this->assertNotContainsMultiple($not_contains, $output);
@@ -306,7 +307,6 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
         'contains' => [],
         'not_contains' => [
           '<drupal-entity data-entity-type="node" data-entity',
-          'This placeholder should not be rendered.',
         ],
       ],
     ];
@@ -376,7 +376,7 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
     $filter_result = $this->filter->process($content, 'en');
     $output = $filter_result->getProcessedText();
     $this->assertContains($this->node->body->value, $output);
-    $this->assertNotContains('This placeholder should not be rendered.', $output);
+    $this->assertEntityEmbedFilterHasRun($output);
   }
 
   /**
@@ -405,7 +405,7 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
 
     $file_path = file_url_transform_relative(file_create_url($image->getFileUri()));
     $this->assertContains($file_path, $output);
-    $this->assertNotContains('This placeholder should not be rendered.', $output);
+    $this->assertEntityEmbedFilterHasRun($output);
 
     $dom = Html::load($output);
     $xpath = new \DOMXPath($dom);
@@ -441,7 +441,7 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
     /** @var \Drupal\filter\FilterProcessResult $filter_result */
     $filter_result = $this->filter->process($content, 'en');
     $output = $filter_result->getProcessedText();
-    $this->assertNotContains('This placeholder should not be rendered.', $output);
+    $this->assertEntityEmbedFilterHasRun($output);
 
     $dom = Html::load($output);
     $xpath = new \DOMXPath($dom);
@@ -552,7 +552,7 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
     $filter_result = $this->filter->process($input, 'en');
     $output = $filter_result->getProcessedText();
     $this->assertNotContains('drupal-entity data-entity-type="media" data-entity', $output);
-    $this->assertNotContains('This placeholder should not be rendered.', $output);
+    $this->assertEntityEmbedFilterHasRun($output);
     $dom = Html::load($output);
     $xpath = new \DOMXPath($dom);
 
@@ -669,25 +669,6 @@ class EntityEmbedFilterTest extends EntityEmbedFilterTestBase {
     }
   }
 
-  /**
-   * Get an embed code with given attributes.
-   *
-   * @param array $attributes
-   *   The attributes to add.
-   *
-   * @return string
-   *   A string containing a drupal-entity dom element.
-   */
-  public function createEmbedCode(array $attributes) {
-    $dom = Html::load('<drupal-entity>This placeholder should not be rendered.</drupal-entity>');
-    $xpath = new \DOMXPath($dom);
-    $drupal_entity = $xpath->query('//drupal-entity')[0];
-    foreach ($attributes as $attribute => $value) {
-      $drupal_entity->setAttribute($attribute, $value);
-    }
-    return Html::serialize($dom);
-  }
-
   /**
    * Retrieves a sample file of the specified type.
    */
diff --git a/tests/src/Kernel/EntityEmbedFilterTestBase.php b/tests/src/Kernel/EntityEmbedFilterTestBase.php
index 9c87004..6e2d628 100644
--- a/tests/src/Kernel/EntityEmbedFilterTestBase.php
+++ b/tests/src/Kernel/EntityEmbedFilterTestBase.php
@@ -112,8 +112,10 @@ abstract class EntityEmbedFilterTestBase extends KernelTestBase {
    *
    * @return string
    *   A string containing a drupal-entity dom element.
+   *
+   * @see assertEntityEmbedFilterHasRun()
    */
-  public function createEmbedCode(array $attributes) {
+  protected function createEmbedCode(array $attributes) {
     $dom = Html::load('<drupal-entity>This placeholder should not be rendered.</drupal-entity>');
     $xpath = new \DOMXPath($dom);
     $drupal_entity = $xpath->query('//drupal-entity')[0];
@@ -123,4 +125,16 @@ abstract class EntityEmbedFilterTestBase extends KernelTestBase {
     return Html::serialize($dom);
   }
 
+  /**
+   * Asserts that `@Filter=entity_embed` has been run successfully.
+   *
+   * @param string $output
+   *   The string returned by the filtering process.
+   *
+   * @see \Drupal\Tests\entity_embed\Kernel\EntityEmbedFilterTestBase::createEmbedCode()
+   */
+  protected function assertEntityEmbedFilterHasRun($output) {
+    $this->assertNotContains('This placeholder should not be rendered.', $output);
+  }
+
 }