diff --git a/core/modules/comment/comment.install b/core/modules/comment/comment.install
index 5f2c499..9a50a88 100644
--- a/core/modules/comment/comment.install
+++ b/core/modules/comment/comment.install
@@ -136,8 +136,7 @@ function comment_update_8001() {
  */
 
 /**
- * Adds the new 'view_mode' setting to all view displays using the
- * 'comment_default' formatter.
+ * Add the 'view_mode' setting to displays having 'comment_default' formatter.
  */
 function comment_update_8101() {
   $config_factory = \Drupal::configFactory();
diff --git a/core/modules/comment/src/Tests/CommentInterfaceTest.php b/core/modules/comment/src/Tests/CommentInterfaceTest.php
index 98709e9..f351102 100644
--- a/core/modules/comment/src/Tests/CommentInterfaceTest.php
+++ b/core/modules/comment/src/Tests/CommentInterfaceTest.php
@@ -295,8 +295,7 @@ public function testAutoFilledHtmlSubject() {
   }
 
   /**
-   * Tests the comment field formatter used with non-default comment entity view
-   * mode.
+   * Tests the comment formatter configured with a custom comment view mode.
    */
   public function testViewMode() {
     $this->drupalLogin($this->webUser);
diff --git a/core/modules/comment/src/Tests/Update/CommentUpdateTest.php b/core/modules/comment/src/Tests/Update/CommentUpdateTest.php
index db1cb43..900c319 100644
--- a/core/modules/comment/src/Tests/Update/CommentUpdateTest.php
+++ b/core/modules/comment/src/Tests/Update/CommentUpdateTest.php
@@ -21,7 +21,7 @@ class CommentUpdateTest extends UpdatePathTestBase {
    */
   protected function setDatabaseDumpFiles() {
     $this->databaseDumpFiles = [
-      __DIR__ . '/../../../../system/tests/fixtures/update/drupal-8-rc1.bare.standard.php.gz',
+      __DIR__ . '/../../../../system/tests/fixtures/update/drupal-8-rc1.filled.standard.php.gz',
     ];
   }
 
@@ -36,12 +36,23 @@ public function testCommentUpdate8101() {
     $config = $this->config('core.entity_view_display.node.article.default');
     $this->assertNull($config->get('content.comment.settings.view_mode'));
 
+    // Load the 'node.forum.default' entity view display config, and check that
+    // component 'comment_forum' does not contain the 'view_mode' setting.
+    $config = $this->config('core.entity_view_display.node.forum.default');
+    $this->assertNull($config->get('content.comment_forum.settings.view_mode'));
+
     // Run updates.
     $this->runUpdates();
 
-    // Reload the config, and check that 'view_mode' has the value 'default'.
+    // Check that 'node.article.default' entity view display setting 'view_mode'
+    // has the value 'default'.
     $config = $this->config('core.entity_view_display.node.article.default');
     $this->assertIdentical($config->get('content.comment.settings.view_mode'), 'default');
+
+    // Check that 'node.forum.default' entity view display setting 'view_mode'
+    // has the value 'default'.
+    $config = $this->config('core.entity_view_display.node.forum.default');
+    $this->assertIdentical($config->get('content.comment_forum.settings.view_mode'), 'default');
   }
 
 }
diff --git a/core/modules/comment/tests/src/Kernel/CommentIntegrationTest.php b/core/modules/comment/tests/src/Kernel/CommentIntegrationTest.php
index efde8dd..e326f4c 100644
--- a/core/modules/comment/tests/src/Kernel/CommentIntegrationTest.php
+++ b/core/modules/comment/tests/src/Kernel/CommentIntegrationTest.php
@@ -89,7 +89,7 @@ public function testViewMode() {
     EntityViewDisplay::create([
       'targetEntityType' => 'entity_test',
       'bundle' => 'entity_test',
-      'mode' => 'default'
+      'mode' => 'default',
     ])->setComponent($field_name, $component)->setStatus(TRUE)->save();
 
     $host_display_id = 'entity_test.entity_test.default';
@@ -115,10 +115,11 @@ public function testViewMode() {
     $logged = (bool) Database::getConnection()->select('watchdog')
       ->fields('watchdog', ['wid'])
       ->condition('type', 'system')
-      ->condition('message', "View display '@id': Comment field formatter '@name' was disabled because is using the comment view display '@display' (@mode) that was just disabled.")
+      ->condition('message', "View display '@id': Comment field formatter '@name' was disabled because it is using the comment view display '@display' (@mode) that was just disabled.")
       ->condition('variables', serialize($arguments))
       ->execute()
       ->fetchField();
+    $this->assertTrue($logged);
 
     // Re-enable the comment view display.
     EntityViewDisplay::load($comment_display_id)->setStatus(TRUE)->save();