diff --git a/core/modules/tracker/tests/src/Functional/TrackerCommentTest.php b/core/modules/tracker/tests/src/Functional/TrackerCommentTest.php
new file mode 100644
index 0000000000..0f23bee9b4
--- /dev/null
+++ b/core/modules/tracker/tests/src/Functional/TrackerCommentTest.php
@@ -0,0 +1,306 @@
+<?php
+
+namespace Drupal\Tests\tracker\Functional;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\node\Entity\Node;
+
+/**
+ * Create and delete nodes and check for their display in the tracker listings.
+ *
+ * @group tracker
+ */
+class TrackerCommentTest extends TrackerTest {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'block',
+    'comment',
+    'tracker',
+    'history',
+    'node_test',
+  ];
+
+  /**
+   * Permissions to give to test users.
+   *
+   * @var array
+   */
+  protected $permissions = [
+    'access comments',
+    'create page content',
+    'post comments',
+    'skip comment approval',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->addDefaultCommentField('node', 'page');
+  }
+
+  /**
+   * Tests for the presence of nodes on the global tracker listing.
+   */
+  public function testTrackerAll() {
+    parent::testTrackerAll();
+
+    // Test proper display of time on activity page when comments are disabled.
+    // Disable comments.
+    FieldStorageConfig::loadByName('node', 'comment')->delete();
+    $node = $this->drupalCreateNode([
+      // This title is required to trigger the custom changed time set in the
+      // node_test module. This is needed in order to ensure a sufficiently
+      // large 'time ago' interval that isn't numbered in seconds.
+      'title' => 'testing_node_presave',
+      'status' => 1,
+    ]);
+
+    $this->drupalGet('activity');
+    $this->assertText($node->label(), 'Published node shows up in the tracker listing.');
+    $this->assertText(\Drupal::service('date.formatter')->formatTimeDiffSince($node->getChangedTime()), 'The changed time was displayed on the tracker listing.');
+  }
+
+  /**
+   * Tests for the presence of nodes on a user's tracker listing.
+   */
+  public function testTrackerUser() {
+    parent::testTrackerUser();
+
+    $this->nodes['other_published_no_comment'] = $this->drupalCreateNode([
+      'title' => $this->randomMachineName(8),
+      'uid' => $this->otherUser->id(),
+      'status' => 1,
+    ]);
+    $this->nodes['other_published_my_comment'] = $this->drupalCreateNode([
+      'title' => $this->randomMachineName(8),
+      'uid' => $this->otherUser->id(),
+      'status' => 1,
+    ]);
+    $comment = [
+      'subject[0][value]' => $this->randomMachineName(),
+      'comment_body[0][value]' => $this->randomMachineName(20),
+    ];
+    $this->drupalPostForm('comment/reply/node/' . $this->nodes['other_published_my_comment']->id() . '/comment', $comment, t('Save'));
+
+    $this->drupalGet('user/' . $this->user->id() . '/activity');
+    $this->assertNoText($this->nodes['other_published_no_comment']->label(), "Another user's nodes do not show up in the user's tracker listing.");
+    $this->assertText($this->nodes['other_published_my_comment']->label(), "Nodes that the user has commented on appear in the user's tracker listing.");
+
+    // Assert cache contexts.
+    $this->assertCacheContexts([
+      'languages:language_interface',
+      'route',
+      'theme',
+      'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT,
+      'url.query_args.pagers:0',
+      'user',
+      'user.node_grants:view',
+    ]
+    );
+    // Assert cache tags for the visible nodes (including owners) and node list
+    // cache tag.
+    $expected_tags = Cache::mergeTags($this->nodes['my_published']->getCacheTags(), $this->nodes['my_published']->getOwner()->getCacheTags());
+    $expected_tags = Cache::mergeTags($expected_tags, $this->nodes['other_published_my_comment']->getCacheTags());
+    $expected_tags = Cache::mergeTags($expected_tags, $this->nodes['other_published_my_comment']->getOwner()->getCacheTags());
+    // Because the 'user.permissions' cache context is being optimized away.
+    $role_tags = [];
+    foreach ($this->user->getRoles() as $rid) {
+      $role_tags[] = "config:user.role.$rid";
+    }
+    $expected_tags = Cache::mergeTags($expected_tags, $role_tags);
+    $block_tags = [
+      'block_view',
+      'config:block.block.page_actions_block',
+      'config:block.block.page_tabs_block',
+      'config:block_list',
+    ];
+    $expected_tags = Cache::mergeTags($expected_tags, $block_tags);
+    $additional_tags = [
+      'node_list',
+      'rendered',
+    ];
+    $expected_tags = Cache::mergeTags($expected_tags, $additional_tags);
+
+    $this->assertCacheTags($expected_tags);
+
+    // Verify that unpublished comments are removed from the tracker.
+    $admin_user = $this->drupalCreateUser(['post comments',
+      'administer comments',
+      'access user profiles',
+    ]
+    );
+    $this->drupalLogin($admin_user);
+    $this->drupalPostForm('comment/1/edit', ['status' => CommentInterface::NOT_PUBLISHED], t('Save'));
+    $this->drupalGet('user/' . $this->user->id() . '/activity');
+    $this->assertNoText($this->nodes['other_published_my_comment']->label(), 'Unpublished comments are not counted on the tracker listing.');
+  }
+
+  /**
+   * Tests the metadata for the "new"/"updated" indicators.
+   */
+  public function testTrackerHistoryMetadata() {
+    parent::testTrackerHistoryMetadata();
+
+    // Add a comment to the page, make sure it is created after the node by
+    // sleeping for one second, to ensure the last comment timestamp is
+    // different from before.
+    $comment = [
+      'subject[0][value]' => $this->randomMachineName(),
+      'comment_body[0][value]' => $this->randomMachineName(20),
+    ];
+    sleep(1);
+    $this->drupalPostForm('comment/reply/node/' . $this->node->id() . '/comment', $comment, t('Save'));
+    // Reload the node so that comment.module's hook_node_load()
+    // implementation can set $node->last_comment_timestamp for the freshly
+    // posted comment.
+    $node = Node::load($this->node->id());
+
+    // Verify that the history metadata is updated.
+    $this->drupalGet('activity');
+    $this->assertCommentHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp);
+    $this->drupalGet('activity/' . $this->user->id());
+    $this->assertCommentHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp);
+    $this->drupalGet('user/' . $this->user->id() . '/activity');
+    $this->assertCommentHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp);
+
+    // Log out, now verify that the metadata is still there, but the library is
+    // not.
+    $this->drupalLogout();
+    $this->drupalGet('activity');
+    $this->assertCommentHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp, FALSE);
+    $this->drupalGet('user/' . $this->user->id() . '/activity');
+    $this->assertCommentHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp, FALSE);
+  }
+
+  /**
+   * Tests for ordering on a users tracker listing when comments are posted.
+   */
+  public function testTrackerOrderingNewComments() {
+    $this->drupalLogin($this->user);
+
+    $node_one = $this->drupalCreateNode([
+      'title' => $this->randomMachineName(8),
+    ]);
+
+    $node_two = $this->drupalCreateNode([
+      'title' => $this->randomMachineName(8),
+    ]);
+
+    // Now get otherUser to track these pieces of content.
+    $this->drupalLogin($this->otherUser);
+
+    // Add a comment to the first page.
+    $comment = [
+      'subject[0][value]' => $this->randomMachineName(),
+      'comment_body[0][value]' => $this->randomMachineName(20),
+    ];
+    $this->drupalPostForm('comment/reply/node/' . $node_one->id() . '/comment', $comment, t('Save'));
+
+    // If the comment is posted in the same second as the last one then Drupal
+    // can't tell the difference, so we wait one second here.
+    sleep(1);
+
+    // Add a comment to the second page.
+    $comment = [
+      'subject[0][value]' => $this->randomMachineName(),
+      'comment_body[0][value]' => $this->randomMachineName(20),
+    ];
+    $this->drupalPostForm('comment/reply/node/' . $node_two->id() . '/comment', $comment, t('Save'));
+
+    // We should at this point have in our tracker for otherUser:
+    // 1. node_two
+    // 2. node_one
+    // Because that's the reverse order of the posted comments.
+    // Now we're going to post a comment to node_one which should jump it to the
+    // top of the list.
+    $this->drupalLogin($this->user);
+    // If the comment is posted in the same second as the last one then Drupal
+    // can't tell the difference, so we wait one second here.
+    sleep(1);
+
+    // Add a comment to the second page.
+    $comment = [
+      'subject[0][value]' => $this->randomMachineName(),
+      'comment_body[0][value]' => $this->randomMachineName(20),
+    ];
+    $this->drupalPostForm('comment/reply/node/' . $node_one->id() . '/comment', $comment, t('Save'));
+
+    // Switch back to the otherUser and assert that the order has swapped.
+    $this->drupalLogin($this->otherUser);
+    $this->drupalGet('user/' . $this->otherUser->id() . '/activity');
+    // This is a cheeky way of asserting that the nodes are in the right order
+    // on the tracker page.
+    // It's almost certainly too brittle.
+    $pattern = '/' . preg_quote($node_one->getTitle()) . '.+' . preg_quote($node_two->getTitle()) . '/s';
+    $this->verbose($pattern);
+    $this->assertPattern($pattern, 'Most recently commented on node appears at the top of tracker');
+  }
+
+  /**
+   * Tests that existing nodes are indexed by cron.
+   */
+  public function testTrackerCronIndexing() {
+    $this->drupalLogin($this->user);
+
+    // Create 3 nodes.
+    $edits = [];
+    $nodes = [];
+    for ($i = 1; $i <= 3; $i++) {
+      $edits[$i] = [
+        'title' => $this->randomMachineName(),
+      ];
+      $nodes[$i] = $this->drupalCreateNode($edits[$i]);
+    }
+
+    // Add a comment to the last node as other user.
+    $this->drupalLogin($this->otherUser);
+    $comment = [
+      'subject[0][value]' => $this->randomMachineName(),
+      'comment_body[0][value]' => $this->randomMachineName(20),
+    ];
+    $this->drupalPostForm('comment/reply/node/' . $nodes[3]->id() . '/comment', $comment, t('Save'));
+
+    // Run the tests.
+    $this->doTestTrackerCronIndexing($nodes);
+  }
+
+  /**
+   * Passes if the appropriate history metadata exists.
+   *
+   * Verify the data-history-node-id, data-history-node-timestamp and
+   * data-history-node-last-comment-timestamp attributes, which are used by the
+   * drupal.tracker-history library to add the appropriate "new" and "updated"
+   * indicators, as well as the "x new" replies link to the tracker.
+   * We do this in JavaScript to prevent breaking the render cache.
+   *
+   * @param int $node_id
+   *   A node ID, that must exist as a data-history-node-id attribute.
+   * @param int $node_timestamp
+   *   A node timestamp, that must exist as a data-history-node-timestamp
+   *   attribute.
+   * @param int $node_last_comment_timestamp
+   *   A node's last comment timestamp, that must exist as a
+   *   data-history-node-last-comment-timestamp attribute.
+   * @param bool $library_is_present
+   *   Whether the drupal.tracker-history library should be present or not.
+   */
+  public function assertCommentHistoryMetadata($node_id, $node_timestamp, $node_last_comment_timestamp, $library_is_present = TRUE) {
+    $this->assertHistoryMetadata($node_id, $node_timestamp, $library_is_present);
+    $this->assertIdentical(1, count($this->xpath('//table/tbody/tr/td[@data-history-node-last-comment-timestamp="' . $node_last_comment_timestamp . '"]')), 'Tracker table cell contains the data-history-node-last-comment-timestamp attribute for the node.');
+  }
+
+}
diff --git a/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php b/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php
index e06fd4cd14..3b7d7dab12 100644
--- a/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php
+++ b/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php
@@ -4,6 +4,7 @@
 
 use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
 use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\field\Entity\FieldStorageConfig;
 use Drupal\node\Entity\NodeType;
 use Drupal\Tests\BrowserTestBase;
 
@@ -33,6 +34,9 @@ class TrackerNodeAccessTest extends BrowserTestBase {
    */
   protected $defaultTheme = 'stark';
 
+  /**
+   * {@inheritdoc}
+   */
   protected function setUp(): void {
     parent::setUp();
     node_access_rebuild();
@@ -101,6 +105,9 @@ public function testTrackerNodeAccess() {
     $this->assertSession()->pageTextContains($private_node->getTitle());
     $this->assertSession()->pageTextContains($public_node->getTitle());
 
+    // Comments column displayed.
+    $this->assertSession()->pageTextContains('Comments');
+
     // User without access should not see private node.
     $this->drupalLogin($no_access_user);
     $this->drupalGet('activity');
@@ -109,6 +116,23 @@ public function testTrackerNodeAccess() {
     $this->drupalGet('user/' . $access_user->id() . '/activity');
     $this->assertSession()->pageTextNotContains($private_node->getTitle());
     $this->assertSession()->pageTextContains($public_node->getTitle());
+
+    // Ensure module pages works when comment module uninstalled.
+    $field = FieldStorageConfig::loadByName('node', 'comment');
+    $field->delete();
+    field_purge_batch(10);
+    /** @var \Drupal\Core\Extension\ModuleInstallerInterface $service */
+    $service = \Drupal::service('module_installer');
+    $service->uninstall(['comment']);
+    $this->drupalLogin($access_user);
+    $this->drupalGet('activity');
+    $this->assertSession()->pageTextContains($private_node->getTitle());
+    // Comments column hidden.
+    $this->assertSession()->pageTextNotContains('Comments');
+    $this->drupalGet('user/' . $access_user->id() . '/activity');
+    $this->assertSession()->pageTextContains($private_node->getTitle());
+    // Comments column hidden.
+    $this->assertSession()->pageTextNotContains('Comments');
   }
 
 }
diff --git a/core/modules/tracker/tests/src/Functional/TrackerTest.php b/core/modules/tracker/tests/src/Functional/TrackerTest.php
index c8d9784cb2..e27bcfd7ca 100644
--- a/core/modules/tracker/tests/src/Functional/TrackerTest.php
+++ b/core/modules/tracker/tests/src/Functional/TrackerTest.php
@@ -2,14 +2,10 @@
 
 namespace Drupal\Tests\tracker\Functional;
 
-use Drupal\comment\CommentInterface;
-use Drupal\comment\Tests\CommentTestTrait;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Database\Database;
 use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Session\AccountInterface;
-use Drupal\field\Entity\FieldStorageConfig;
-use Drupal\node\Entity\Node;
 use Drupal\Tests\BrowserTestBase;
 use Drupal\Tests\system\Functional\Cache\AssertPageCacheContextsAndTagsTrait;
 
@@ -20,7 +16,6 @@
  */
 class TrackerTest extends BrowserTestBase {
 
-  use CommentTestTrait;
   use AssertPageCacheContextsAndTagsTrait;
 
   /**
@@ -36,6 +31,13 @@ class TrackerTest extends BrowserTestBase {
     'node_test',
   ];
 
+  /**
+   * Permissions to give to test users.
+   *
+   * @var array
+   */
+  protected $permissions = ['create page content'];
+
   /**
    * {@inheritdoc}
    */
@@ -55,15 +57,16 @@ class TrackerTest extends BrowserTestBase {
    */
   protected $otherUser;
 
+  /**
+   * {@inheritdoc}
+   */
   protected function setUp(): void {
     parent::setUp();
 
     $this->drupalCreateContentType(['type' => 'page', 'name' => 'Basic page']);
 
-    $permissions = ['access comments', 'create page content', 'post comments', 'skip comment approval'];
-    $this->user = $this->drupalCreateUser($permissions);
-    $this->otherUser = $this->drupalCreateUser($permissions);
-    $this->addDefaultCommentField('node', 'page');
+    $this->user = $this->drupalCreateUser($this->permissions);
+    $this->otherUser = $this->drupalCreateUser($this->permissions);
     user_role_grant_permissions(AccountInterface::ANONYMOUS_ROLE, [
       'access content',
       'access user profiles',
@@ -93,7 +96,15 @@ public function testTrackerAll() {
     $this->assertSession()->linkExists('My recent content', 0, 'User tab shows up on the global tracker page.');
 
     // Assert cache contexts, specifically the pager and node access contexts.
-    $this->assertCacheContexts(['languages:language_interface', 'route', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'url.query_args.pagers:0', 'user.node_grants:view', 'user']);
+    $this->assertCacheContexts([
+      'languages:language_interface',
+      'route', 'theme',
+      'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT,
+      'url.query_args.pagers:0',
+      'user.node_grants:view',
+      'user',
+    ]
+    );
     // Assert cache tags for the action/tabs blocks, visible node, and node list
     // cache tag.
     $expected_tags = Cache::mergeTags($published->getCacheTags(), $published->getOwner()->getCacheTags());
@@ -123,20 +134,6 @@ public function testTrackerAll() {
     $this->drupalGet('activity');
     $this->assertSession()->pageTextNotContains($published->label());
 
-    // Test proper display of time on activity page when comments are disabled.
-    // Disable comments.
-    FieldStorageConfig::loadByName('node', 'comment')->delete();
-    $node = $this->drupalCreateNode([
-      // This title is required to trigger the custom changed time set in the
-      // node_test module. This is needed in order to ensure a sufficiently
-      // large 'time ago' interval that isn't numbered in seconds.
-      'title' => 'testing_node_presave',
-      'status' => 1,
-    ]);
-
-    $this->drupalGet('activity');
-    $this->assertSession()->pageTextContains($node->label());
-    $this->assertSession()->pageTextContains(\Drupal::service('date.formatter')->formatTimeDiffSince($node->getChangedTime()));
   }
 
   /**
@@ -145,46 +142,35 @@ public function testTrackerAll() {
   public function testTrackerUser() {
     $this->drupalLogin($this->user);
 
-    $unpublished = $this->drupalCreateNode([
+    $this->nodes = [];
+    $this->nodes['unpublished'] = $this->drupalCreateNode([
       'title' => $this->randomMachineName(8),
       'uid' => $this->user->id(),
       'status' => 0,
     ]);
-    $my_published = $this->drupalCreateNode([
+    $this->nodes['my_published'] = $this->drupalCreateNode([
       'title' => $this->randomMachineName(8),
       'uid' => $this->user->id(),
       'status' => 1,
     ]);
-    $other_published_no_comment = $this->drupalCreateNode([
-      'title' => $this->randomMachineName(8),
-      'uid' => $this->otherUser->id(),
-      'status' => 1,
-    ]);
-    $other_published_my_comment = $this->drupalCreateNode([
-      'title' => $this->randomMachineName(8),
-      'uid' => $this->otherUser->id(),
-      'status' => 1,
-    ]);
-    $comment = [
-      'subject[0][value]' => $this->randomMachineName(),
-      'comment_body[0][value]' => $this->randomMachineName(20),
-    ];
-    $this->drupalGet('comment/reply/node/' . $other_published_my_comment->id() . '/comment');
-    $this->submitForm($comment, 'Save');
 
     $this->drupalGet('user/' . $this->user->id() . '/activity');
-    $this->assertSession()->pageTextNotContains($unpublished->label());
-    $this->assertSession()->pageTextContains($my_published->label());
-    $this->assertSession()->pageTextNotContains($other_published_no_comment->label());
-    $this->assertSession()->pageTextContains($other_published_my_comment->label());
+    $this->assertNoText($this->nodes['unpublished']->label(), "Unpublished nodes do not show up in the user's tracker listing.");
+    $this->assertText($this->nodes['my_published']->label(), "Published nodes show up in the user's tracker listing.");
 
     // Assert cache contexts.
-    $this->assertCacheContexts(['languages:language_interface', 'route', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'url.query_args.pagers:0', 'user', 'user.node_grants:view']);
+    $this->assertCacheContexts([
+      'languages:language_interface',
+      'route', 'theme',
+      'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT,
+      'url.query_args.pagers:0',
+      'user',
+      'user.node_grants:view',
+    ]
+    );
     // Assert cache tags for the visible nodes (including owners) and node list
     // cache tag.
-    $expected_tags = Cache::mergeTags($my_published->getCacheTags(), $my_published->getOwner()->getCacheTags());
-    $expected_tags = Cache::mergeTags($expected_tags, $other_published_my_comment->getCacheTags());
-    $expected_tags = Cache::mergeTags($expected_tags, $other_published_my_comment->getOwner()->getCacheTags());
+    $expected_tags = Cache::mergeTags($this->nodes['my_published']->getCacheTags(), $this->nodes['my_published']->getOwner()->getCacheTags());
     // Because the 'user.permissions' cache context is being optimized away.
     $role_tags = [];
     foreach ($this->user->getRoles() as $rid) {
@@ -206,26 +192,23 @@ public function testTrackerUser() {
     $expected_tags = Cache::mergeTags($expected_tags, $additional_tags);
 
     $this->assertCacheTags($expected_tags);
-    $this->assertCacheContexts(['languages:language_interface', 'route', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'url.query_args.pagers:0', 'user', 'user.node_grants:view']);
-
-    $this->assertSession()->linkExists($my_published->label());
-    $this->assertSession()->linkNotExists($unpublished->label());
+    $this->assertCacheContexts([
+      'languages:language_interface',
+      'route',
+      'theme',
+      'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT,
+      'url.query_args.pagers:0',
+      'user',
+      'user.node_grants:view',
+    ]
+    );
+
+    $this->assertSession()->linkExists($this->nodes['my_published']->label());
+    $this->assertSession()->linkNotExists($this->nodes['unpublished']->label());
     // Verify that title and tab title have been set correctly.
     $this->assertSession()->pageTextContains('Activity');
     $this->assertSession()->titleEquals($this->user->getAccountName() . ' | Drupal');
 
-    // Verify that unpublished comments are removed from the tracker.
-    $admin_user = $this->drupalCreateUser([
-      'post comments',
-      'administer comments',
-      'access user profiles',
-    ]);
-    $this->drupalLogin($admin_user);
-    $this->drupalGet('comment/1/edit');
-    $this->submitForm(['status' => CommentInterface::NOT_PUBLISHED], 'Save');
-    $this->drupalGet('user/' . $this->user->id() . '/activity');
-    $this->assertSession()->pageTextNotContains($other_published_my_comment->label());
-
     // Test escaping of title on user's tracker tab.
     \Drupal::service('module_installer')->install(['user_hooks_test']);
     Cache::invalidateTags(['rendered']);
@@ -250,116 +233,16 @@ public function testTrackerHistoryMetadata() {
     $edit = [
       'title' => $this->randomMachineName(8),
     ];
-    $node = $this->drupalCreateNode($edit);
+    $this->node = $this->drupalCreateNode($edit);
 
     // Verify that the history metadata is present.
     $this->drupalGet('activity');
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->getChangedTime());
+    $this->assertHistoryMetadata($this->node->id(), $this->node->getChangedTime());
     $this->drupalGet('activity/' . $this->user->id());
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->getChangedTime());
+    $this->assertHistoryMetadata($this->node->id(), $this->node->getChangedTime());
     $this->drupalGet('user/' . $this->user->id() . '/activity');
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->getChangedTime());
-
-    // Add a comment to the page, make sure it is created after the node by
-    // sleeping for one second, to ensure the last comment timestamp is
-    // different from before.
-    $comment = [
-      'subject[0][value]' => $this->randomMachineName(),
-      'comment_body[0][value]' => $this->randomMachineName(20),
-    ];
-    sleep(1);
-    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment');
-    $this->submitForm($comment, 'Save');
-    // Reload the node so that comment.module's hook_node_load()
-    // implementation can set $node->last_comment_timestamp for the freshly
-    // posted comment.
-    $node = Node::load($node->id());
-
-    // Verify that the history metadata is updated.
-    $this->drupalGet('activity');
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp);
-    $this->drupalGet('activity/' . $this->user->id());
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp);
-    $this->drupalGet('user/' . $this->user->id() . '/activity');
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp);
-
-    // Log out, now verify that the metadata is still there, but the library is
-    // not.
-    $this->drupalLogout();
-    $this->drupalGet('activity');
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp, FALSE);
-    $this->drupalGet('user/' . $this->user->id() . '/activity');
-    $this->assertHistoryMetadata($node->id(), $node->getChangedTime(), $node->get('comment')->last_comment_timestamp, FALSE);
-  }
-
-  /**
-   * Tests for ordering on a users tracker listing when comments are posted.
-   */
-  public function testTrackerOrderingNewComments() {
-    $this->drupalLogin($this->user);
-
-    $node_one = $this->drupalCreateNode([
-      'title' => $this->randomMachineName(8),
-    ]);
-
-    $node_two = $this->drupalCreateNode([
-      'title' => $this->randomMachineName(8),
-    ]);
-
-    // Now get otherUser to track these pieces of content.
-    $this->drupalLogin($this->otherUser);
+    $this->assertHistoryMetadata($this->node->id(), $this->node->getChangedTime());
 
-    // Add a comment to the first page.
-    $comment = [
-      'subject[0][value]' => $this->randomMachineName(),
-      'comment_body[0][value]' => $this->randomMachineName(20),
-    ];
-    $this->drupalGet('comment/reply/node/' . $node_one->id() . '/comment');
-    $this->submitForm($comment, 'Save');
-
-    // If the comment is posted in the same second as the last one then Drupal
-    // can't tell the difference, so we wait one second here.
-    sleep(1);
-
-    // Add a comment to the second page.
-    $comment = [
-      'subject[0][value]' => $this->randomMachineName(),
-      'comment_body[0][value]' => $this->randomMachineName(20),
-    ];
-    $this->drupalGet('comment/reply/node/' . $node_two->id() . '/comment');
-    $this->submitForm($comment, 'Save');
-
-    // We should at this point have in our tracker for otherUser:
-    // 1. node_two
-    // 2. node_one
-    // Because that's the reverse order of the posted comments.
-
-    // Now we're going to post a comment to node_one which should jump it to the
-    // top of the list.
-
-    $this->drupalLogin($this->user);
-    // If the comment is posted in the same second as the last one then Drupal
-    // can't tell the difference, so we wait one second here.
-    sleep(1);
-
-    // Add a comment to the second page.
-    $comment = [
-      'subject[0][value]' => $this->randomMachineName(),
-      'comment_body[0][value]' => $this->randomMachineName(20),
-    ];
-    $this->drupalGet('comment/reply/node/' . $node_one->id() . '/comment');
-    $this->submitForm($comment, 'Save');
-
-    // Switch back to the otherUser and assert that the order has swapped.
-    $this->drupalLogin($this->otherUser);
-    $this->drupalGet('user/' . $this->otherUser->id() . '/activity');
-    // This is a cheeky way of asserting that the nodes are in the right order
-    // on the tracker page.
-    // It's almost certainly too brittle.
-    $pattern = '/' . preg_quote($node_one->getTitle()) . '.+' . preg_quote($node_two->getTitle()) . '/s';
-    // Verify that the most recent comment on node appears at the top of
-    // tracker.
-    $this->assertSession()->responseMatches($pattern);
   }
 
   /**
@@ -378,15 +261,6 @@ public function testTrackerCronIndexing() {
       $nodes[$i] = $this->drupalCreateNode($edits[$i]);
     }
 
-    // Add a comment to the last node as other user.
-    $this->drupalLogin($this->otherUser);
-    $comment = [
-      'subject[0][value]' => $this->randomMachineName(),
-      'comment_body[0][value]' => $this->randomMachineName(20),
-    ];
-    $this->drupalGet('comment/reply/node/' . $nodes[3]->id() . '/comment');
-    $this->submitForm($comment, 'Save');
-
     // Create an unpublished node.
     $unpublished = $this->drupalCreateNode([
       'title' => $this->randomMachineName(8),
@@ -395,7 +269,21 @@ public function testTrackerCronIndexing() {
 
     $this->drupalGet('activity');
     $this->assertSession()->responseNotContains($unpublished->label());
+    // Run the tests.
+    $this->doTestTrackerCronIndexing($nodes);
+  }
 
+  /**
+   * Runs assertions for testTrackerCronIndexing().
+   *
+   * This has been moved into a separate method to ease tests of the submethod
+   * \Drupal\Tests\tracker\Functional\TrackerCommentTest::testTrackerCronIndexing()
+   * and reduce code duplication.
+   *
+   * @param \Drupal\node\Entity\Node[] $nodes
+   *   The created nodes to test.
+   */
+  protected function doTestTrackerCronIndexing(array $nodes) {
     // Start indexing backwards from node 4.
     \Drupal::state()->set('tracker.index_nid', 4);
 
@@ -461,26 +349,22 @@ public function testTrackerAdminUnpublish() {
   /**
    * Passes if the appropriate history metadata exists.
    *
-   * Verify the data-history-node-id, data-history-node-timestamp and
-   * data-history-node-last-comment-timestamp attributes, which are used by the
-   * drupal.tracker-history library to add the appropriate "new" and "updated"
-   * indicators, as well as the "x new" replies link to the tracker.
-   * We do this in JavaScript to prevent breaking the render cache.
+   * Verify the data-history-node-id, data-history-node-timestamp attribute,
+   * which is used by the drupal.tracker-history library to add the appropriate
+   * "new" and "updated" indicators, as well as the "x new" replies link to the
+   * tracker. We do this in JavaScript to prevent breaking the render cache.
    *
    * @param int $node_id
-   *   A node ID, that must exist as a data-history-node-id attribute
+   *   A node ID, that must exist as a data-history-node-id attribute.
    * @param int $node_timestamp
    *   A node timestamp, that must exist as a data-history-node-timestamp
    *   attribute.
-   * @param int $node_last_comment_timestamp
-   *   A node's last comment timestamp, that must exist as a
-   *   data-history-node-last-comment-timestamp attribute.
    * @param bool $library_is_present
    *   Whether the drupal.tracker-history library should be present or not.
    *
    * @internal
    */
-  public function assertHistoryMetadata(int $node_id, int $node_timestamp, int $node_last_comment_timestamp, bool $library_is_present = TRUE): void {
+  public function assertHistoryMetadata($node_id, $node_timestamp, $library_is_present = TRUE) {
     $settings = $this->getDrupalSettings();
     $this->assertSame($library_is_present, isset($settings['ajaxPageState']) && in_array('tracker/history', explode(',', $settings['ajaxPageState']['libraries'])), 'drupal.tracker-history library is present.');
     $this->assertCount(1, $this->xpath('//table/tbody/tr/td[@data-history-node-id="' . $node_id . '" and @data-history-node-timestamp="' . $node_timestamp . '"]'), 'Tracker table cell contains the data-history-node-id and data-history-node-timestamp attributes for the node.');
diff --git a/core/modules/tracker/tests/src/Kernel/Migrate/d7/MigrateTrackerSettingsTest.php b/core/modules/tracker/tests/src/Kernel/Migrate/d7/MigrateTrackerSettingsTest.php
index fa3b1daa12..c7f8861c31 100644
--- a/core/modules/tracker/tests/src/Kernel/Migrate/d7/MigrateTrackerSettingsTest.php
+++ b/core/modules/tracker/tests/src/Kernel/Migrate/d7/MigrateTrackerSettingsTest.php
@@ -11,6 +11,11 @@
  */
 class MigrateTrackerSettingsTest extends MigrateDrupal7TestBase {
 
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
   protected static $modules = ['tracker'];
 
   /**
diff --git a/core/modules/tracker/tracker.info.yml b/core/modules/tracker/tracker.info.yml
index 4f1718f09f..d4abe184a2 100644
--- a/core/modules/tracker/tracker.info.yml
+++ b/core/modules/tracker/tracker.info.yml
@@ -3,6 +3,5 @@ type: module
 description: 'Enables tracking of recent content for users.'
 dependencies:
   - drupal:node
-  - drupal:comment
 package: Core
 version: VERSION
diff --git a/core/modules/tracker/tracker.module b/core/modules/tracker/tracker.module
index 8dbc5ac2f2..9aa31eb13b 100644
--- a/core/modules/tracker/tracker.module
+++ b/core/modules/tracker/tracker.module
@@ -91,29 +91,29 @@ function tracker_cron() {
 
       // Insert the user-level data for the commenters (except if a commenter
       // is the node's author).
-
       // Get unique user IDs via entityQueryAggregate because it's the easiest
       // database agnostic way. We don't actually care about the comments here
       // so don't add an aggregate field.
-      $result = \Drupal::entityQueryAggregate('comment')
-        ->accessCheck(FALSE)
-        ->condition('entity_type', 'node')
-        ->condition('entity_id', $node->id())
-        ->condition('uid', $node->getOwnerId(), '<>')
-        ->condition('status', CommentInterface::PUBLISHED)
-        ->groupBy('uid')
-        ->execute();
-      if ($result) {
-        $query = $connection->insert('tracker_user');
-        foreach ($result as $row) {
-          $query->fields([
-            'uid' => $row['uid'],
-            'nid' => $nid,
-            'published' => CommentInterface::PUBLISHED,
-            'changed' => $changed,
-          ]);
+      if (\Drupal::moduleHandler()->moduleExists('comment')) {
+        $result = \Drupal::entityQueryAggregate('comment')
+          ->condition('entity_type', 'node')
+          ->condition('entity_id', $node->id())
+          ->condition('uid', $node->getOwnerId(), '<>')
+          ->condition('status', CommentInterface::PUBLISHED)
+          ->groupBy('uid')
+          ->execute();
+        if ($result) {
+          $query = db_insert('tracker_user');
+          foreach ($result as $row) {
+            $query->fields([
+              'uid' => $row['uid'],
+              'nid' => $nid,
+              'published' => CommentInterface::PUBLISHED,
+              'changed' => $changed,
+            ]);
+          }
+          $query->execute();
         }
-        $query->execute();
       }
 
       // Note that we have indexed at least one node.
@@ -263,11 +263,13 @@ function _tracker_add($nid, $uid, $changed) {
  * @todo Check if we should introduce 'language context' here, because the
  *   callers may need different timestamps depending on the users' language?
  */
-function _tracker_calculate_changed($node) {
+function _tracker_calculate_changed(NodeInterface $node) {
   $changed = $node->getChangedTime();
-  $latest_comment = \Drupal::service('comment.statistics')->read([$node], 'node', FALSE);
-  if ($latest_comment && $latest_comment->last_comment_timestamp > $changed) {
-    $changed = $latest_comment->last_comment_timestamp;
+  if (\Drupal::hasService('comment.statistics')) {
+    $latest_comment = \Drupal::service('comment.statistics')->read([$node], 'node', FALSE);
+    if ($latest_comment && $latest_comment->last_comment_timestamp > $changed) {
+      $changed = $latest_comment->last_comment_timestamp;
+    }
   }
   return $changed;
 }
@@ -321,7 +323,6 @@ function _tracker_remove($nid, $uid = NULL, $changed = NULL) {
     if ($tracker_node && $changed >= $tracker_node->changed) {
       // If we're here, the item being removed is *possibly* the item that
       // established the node's changed timestamp.
-
       // We just have to recalculate things from scratch.
       $changed = _tracker_calculate_changed($node);
 
diff --git a/core/modules/tracker/tracker.views.inc b/core/modules/tracker/tracker.views.inc
index be15d57478..4422f4605f 100644
--- a/core/modules/tracker/tracker.views.inc
+++ b/core/modules/tracker/tracker.views.inc
@@ -157,7 +157,7 @@ function tracker_views_data() {
  * Implements hook_views_data_alter().
  */
 function tracker_views_data_alter(&$data) {
-  // Provide additional uid_touch handlers which are handled by tracker
+  // Provide additional uid_touch handlers which are handled by tracker.
   $data['node_field_data']['uid_touch_tracker'] = [
     'group' => t('Tracker - User'),
     'title' => t('User posted or commented'),