.../FunctionalJavascript/CKEditorIntegrationTest.php    | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php b/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
index 8bde4b4..c0e19e9 100644
--- a/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
+++ b/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
@@ -177,7 +177,9 @@ class CKEditorIntegrationTest extends EntityEmbedTestBase {
     // operational entity embedding experience in the text editor.
     $this->drupalGet('/node/add/page');
     $this->waitForEditor();
+    $this->assertSame(1, $this->getCkeditorUndoSnapshotCount());
     $this->getSession()->executeScript("CKEDITOR.instances['edit-body-0-value'].setData('<p>Goodbye world!</p>');");
+    $this->assertSame(2, $this->getCkeditorUndoSnapshotCount());
     $this->assignNameToCkeditorIframe();
     $this->getSession()->switchToIFrame('ckeditor');
     $this->assertSession()->pageTextNotContains('Billy Bones');
@@ -197,6 +199,7 @@ class CKEditorIntegrationTest extends EntityEmbedTestBase {
     $this->getSession()->switchToIFrame('ckeditor');
     $this->assertSession()->pageTextContains('Billy Bones');
     $this->getSession()->switchToIFrame();
+    $this->assertSame(3, $this->getCkeditorUndoSnapshotCount());
     $this->getSession()
       ->getPage()
       ->find('css', 'input[name="title[0][value]"]')
@@ -280,4 +283,18 @@ class CKEditorIntegrationTest extends EntityEmbedTestBase {
     $this->getSession()->switchToIFrame();
   }
 
+  /**
+   * Get a CKEditor instance's undo snapshot count.
+   *
+   * @param string $instance_id
+   *   The CKEditor instance ID.
+   *
+   * @return int
+   *   The undo snapshot count.
+   */
+  protected function getCkeditorUndoSnapshotCount($instance_id = 'edit-body-0-value') {
+    $this->waitForEditor($instance_id);
+    return $this->getSession()->evaluateScript("CKEDITOR.instances['$instance_id'].undoManager.snapshots.length");
+  }
+
 }