diff --git a/core/modules/aggregator/src/Tests/AggregatorTestBase.php b/core/modules/aggregator/src/Tests/AggregatorTestBase.php
deleted file mode 100644
index f42248975a..0000000000
--- a/core/modules/aggregator/src/Tests/AggregatorTestBase.php
+++ /dev/null
@@ -1,382 +0,0 @@
-<?php
-
-namespace Drupal\aggregator\Tests;
-
-use Drupal\aggregator\Entity\Feed;
-use Drupal\Component\Utility\Html;
-use Drupal\simpletest\WebTestBase;
-use Drupal\aggregator\FeedInterface;
-
-/**
- * Defines a base class for testing the Aggregator module.
- *
- * @deprecated Scheduled for removal in Drupal 9.0.0.
- *   Use \Drupal\Tests\aggregator\Functional\AggregatorTestBase instead.
- */
-abstract class AggregatorTestBase extends WebTestBase {
-
-  /**
-   * A user with permission to administer feeds and create content.
-   *
-   * @var \Drupal\user\Entity\User
-   */
-  protected $adminUser;
-
-  /**
-   * Modules to install.
-   *
-   * @var array
-   */
-  public static $modules = ['block', 'node', 'aggregator', 'aggregator_test', 'views'];
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-
-    // Create an Article node type.
-    if ($this->profile != 'standard') {
-      $this->drupalCreateContentType(['type' => 'article', 'name' => 'Article']);
-    }
-
-    $this->adminUser = $this->drupalCreateUser(['access administration pages', 'administer news feeds', 'access news feeds', 'create article content']);
-    $this->drupalLogin($this->adminUser);
-    $this->drupalPlaceBlock('local_tasks_block');
-  }
-
-  /**
-   * Creates an aggregator feed.
-   *
-   * This method simulates the form submission on path aggregator/sources/add.
-   *
-   * @param string $feed_url
-   *   (optional) If given, feed will be created with this URL, otherwise
-   *   /rss.xml will be used. Defaults to NULL.
-   * @param array $edit
-   *   Array with additional form fields.
-   *
-   * @return \Drupal\aggregator\FeedInterface
-   *   Full feed object if possible.
-   *
-   * @see getFeedEditArray()
-   */
-  public function createFeed($feed_url = NULL, array $edit = []) {
-    $edit = $this->getFeedEditArray($feed_url, $edit);
-    $this->drupalPostForm('aggregator/sources/add', $edit, t('Save'));
-    $this->assertText(t('The feed @name has been added.', ['@name' => $edit['title[0][value]']]), format_string('The feed @name has been added.', ['@name' => $edit['title[0][value]']]));
-
-    // Verify that the creation message contains a link to a feed.
-    $view_link = $this->xpath('//div[@class="messages"]//a[contains(@href, :href)]', [':href' => 'aggregator/sources/']);
-    $this->assert(isset($view_link), 'The message area contains a link to a feed');
-
-    $fid = db_query("SELECT fid FROM {aggregator_feed} WHERE title = :title AND url = :url", [':title' => $edit['title[0][value]'], ':url' => $edit['url[0][value]']])->fetchField();
-    $this->assertTrue(!empty($fid), 'The feed found in database.');
-    return Feed::load($fid);
-  }
-
-  /**
-   * Deletes an aggregator feed.
-   *
-   * @param \Drupal\aggregator\FeedInterface $feed
-   *   Feed object representing the feed.
-   */
-  public function deleteFeed(FeedInterface $feed) {
-    $this->drupalPostForm('aggregator/sources/' . $feed->id() . '/delete', [], t('Delete'));
-    $this->assertRaw(t('The feed %title has been deleted.', ['%title' => $feed->label()]), 'Feed deleted successfully.');
-  }
-
-  /**
-   * Returns a randomly generated feed edit array.
-   *
-   * @param string $feed_url
-   *   (optional) If given, feed will be created with this URL, otherwise
-   *   /rss.xml will be used. Defaults to NULL.
-   * @param array $edit
-   *   Array with additional form fields.
-   *
-   * @return array
-   *   A feed array.
-   */
-  public function getFeedEditArray($feed_url = NULL, array $edit = []) {
-    $feed_name = $this->randomMachineName(10);
-    if (!$feed_url) {
-      $feed_url = \Drupal::url('view.frontpage.feed_1', [], [
-        'query' => ['feed' => $feed_name],
-        'absolute' => TRUE,
-      ]);
-    }
-    $edit += [
-      'title[0][value]' => $feed_name,
-      'url[0][value]' => $feed_url,
-      'refresh' => '900',
-    ];
-    return $edit;
-  }
-
-  /**
-   * Returns a randomly generated feed edit object.
-   *
-   * @param string $feed_url
-   *   (optional) If given, feed will be created with this URL, otherwise
-   *   /rss.xml will be used. Defaults to NULL.
-   * @param array $values
-   *   (optional) Default values to initialize object properties with.
-   *
-   * @return \Drupal\aggregator\FeedInterface
-   *   A feed object.
-   */
-  public function getFeedEditObject($feed_url = NULL, array $values = []) {
-    $feed_name = $this->randomMachineName(10);
-    if (!$feed_url) {
-      $feed_url = \Drupal::url('view.frontpage.feed_1', [
-        'query' => ['feed' => $feed_name],
-        'absolute' => TRUE,
-      ]);
-    }
-    $values += [
-      'title' => $feed_name,
-      'url' => $feed_url,
-      'refresh' => '900',
-    ];
-    return Feed::create($values);
-  }
-
-  /**
-   * Returns the count of the randomly created feed array.
-   *
-   * @return int
-   *   Number of feed items on default feed created by createFeed().
-   */
-  public function getDefaultFeedItemCount() {
-    // Our tests are based off of rss.xml, so let's find out how many elements should be related.
-    $feed_count = db_query_range('SELECT COUNT(DISTINCT nid) FROM {node_field_data} n WHERE n.promote = 1 AND n.status = 1', 0, $this->config('system.rss')->get('items.limit'))->fetchField();
-    return $feed_count > 10 ? 10 : $feed_count;
-  }
-
-  /**
-   * Updates the feed items.
-   *
-   * This method simulates a click to
-   * admin/config/services/aggregator/update/$fid.
-   *
-   * @param \Drupal\aggregator\FeedInterface $feed
-   *   Feed object representing the feed.
-   * @param int|null $expected_count
-   *   Expected number of feed items. If omitted no check will happen.
-   */
-  public function updateFeedItems(FeedInterface $feed, $expected_count = NULL) {
-    // First, let's ensure we can get to the rss xml.
-    $this->drupalGet($feed->getUrl());
-    $this->assertResponse(200, format_string(':url is reachable.', [':url' => $feed->getUrl()]));
-
-    // Attempt to access the update link directly without an access token.
-    $this->drupalGet('admin/config/services/aggregator/update/' . $feed->id());
-    $this->assertResponse(403);
-
-    // Refresh the feed (simulated link click).
-    $this->drupalGet('admin/config/services/aggregator');
-    $this->clickLink('Update items');
-
-    // Ensure we have the right number of items.
-    $result = db_query('SELECT iid FROM {aggregator_item} WHERE fid = :fid', [':fid' => $feed->id()]);
-    $feed->items = [];
-    foreach ($result as $item) {
-      $feed->items[] = $item->iid;
-    }
-
-    if ($expected_count !== NULL) {
-      $feed->item_count = count($feed->items);
-      $this->assertEqual($expected_count, $feed->item_count, format_string('Total items in feed equal to the total items in database (@val1 != @val2)', ['@val1' => $expected_count, '@val2' => $feed->item_count]));
-    }
-  }
-
-  /**
-   * Confirms an item removal from a feed.
-   *
-   * @param \Drupal\aggregator\FeedInterface $feed
-   *   Feed object representing the feed.
-   */
-  public function deleteFeedItems(FeedInterface $feed) {
-    $this->drupalPostForm('admin/config/services/aggregator/delete/' . $feed->id(), [], t('Delete items'));
-    $this->assertRaw(t('The news items from %title have been deleted.', ['%title' => $feed->label()]), 'Feed items deleted.');
-  }
-
-  /**
-   * Adds and deletes feed items and ensure that the count is zero.
-   *
-   * @param \Drupal\aggregator\FeedInterface $feed
-   *   Feed object representing the feed.
-   * @param int $expected_count
-   *   Expected number of feed items.
-   */
-  public function updateAndDelete(FeedInterface $feed, $expected_count) {
-    $this->updateFeedItems($feed, $expected_count);
-    $count = db_query('SELECT COUNT(*) FROM {aggregator_item} WHERE fid = :fid', [':fid' => $feed->id()])->fetchField();
-    $this->assertTrue($count);
-    $this->deleteFeedItems($feed);
-    $count = db_query('SELECT COUNT(*) FROM {aggregator_item} WHERE fid = :fid', [':fid' => $feed->id()])->fetchField();
-    $this->assertTrue($count == 0);
-  }
-
-  /**
-   * Checks whether the feed name and URL are unique.
-   *
-   * @param string $feed_name
-   *   String containing the feed name to check.
-   * @param string $feed_url
-   *   String containing the feed url to check.
-   *
-   * @return bool
-   *   TRUE if feed is unique.
-   */
-  public function uniqueFeed($feed_name, $feed_url) {
-    $result = db_query("SELECT COUNT(*) FROM {aggregator_feed} WHERE title = :title AND url = :url", [':title' => $feed_name, ':url' => $feed_url])->fetchField();
-    return (1 == $result);
-  }
-
-  /**
-   * Creates a valid OPML file from an array of feeds.
-   *
-   * @param array $feeds
-   *   An array of feeds.
-   *
-   * @return string
-   *   Path to valid OPML file.
-   */
-  public function getValidOpml(array $feeds) {
-    // Properly escape URLs so that XML parsers don't choke on them.
-    foreach ($feeds as &$feed) {
-      $feed['url[0][value]'] = Html::escape($feed['url[0][value]']);
-    }
-    /**
-     * Does not have an XML declaration, must pass the parser.
-     */
-    $opml = <<<EOF
-<opml version="1.0">
-  <head></head>
-  <body>
-    <!-- First feed to be imported. -->
-    <outline text="{$feeds[0]['title[0][value]']}" xmlurl="{$feeds[0]['url[0][value]']}" />
-
-    <!-- Second feed. Test string delimitation and attribute order. -->
-    <outline xmlurl='{$feeds[1]['url[0][value]']}' text='{$feeds[1]['title[0][value]']}'/>
-
-    <!-- Test for duplicate URL and title. -->
-    <outline xmlurl="{$feeds[0]['url[0][value]']}" text="Duplicate URL"/>
-    <outline xmlurl="http://duplicate.title" text="{$feeds[1]['title[0][value]']}"/>
-
-    <!-- Test that feeds are only added with required attributes. -->
-    <outline text="{$feeds[2]['title[0][value]']}" />
-    <outline xmlurl="{$feeds[2]['url[0][value]']}" />
-  </body>
-</opml>
-EOF;
-
-    $path = 'public://valid-opml.xml';
-    // Add the UTF-8 byte order mark.
-    return file_unmanaged_save_data(chr(239) . chr(187) . chr(191) . $opml, $path);
-  }
-
-  /**
-   * Creates an invalid OPML file.
-   *
-   * @return string
-   *   Path to invalid OPML file.
-   */
-  public function getInvalidOpml() {
-    $opml = <<<EOF
-<opml>
-  <invalid>
-</opml>
-EOF;
-
-    $path = 'public://invalid-opml.xml';
-    return file_unmanaged_save_data($opml, $path);
-  }
-
-  /**
-   * Creates a valid but empty OPML file.
-   *
-   * @return string
-   *   Path to empty OPML file.
-   */
-  public function getEmptyOpml() {
-    $opml = <<<EOF
-<?xml version="1.0" encoding="utf-8"?>
-<opml version="1.0">
-  <head></head>
-  <body>
-    <outline text="Sample text" />
-    <outline text="Sample text" url="Sample URL" />
-  </body>
-</opml>
-EOF;
-
-    $path = 'public://empty-opml.xml';
-    return file_unmanaged_save_data($opml, $path);
-  }
-
-  /**
-   * Returns a example RSS091 feed.
-   *
-   * @return string
-   *   Path to the feed.
-   */
-  public function getRSS091Sample() {
-    return $GLOBALS['base_url'] . '/' . drupal_get_path('module', 'aggregator') . '/tests/modules/aggregator_test/aggregator_test_rss091.xml';
-  }
-
-  /**
-   * Returns a example Atom feed.
-   *
-   * @return string
-   *   Path to the feed.
-   */
-  public function getAtomSample() {
-    // The content of this sample ATOM feed is based directly off of the
-    // example provided in RFC 4287.
-    return $GLOBALS['base_url'] . '/' . drupal_get_path('module', 'aggregator') . '/tests/modules/aggregator_test/aggregator_test_atom.xml';
-  }
-
-  /**
-   * Returns a example feed.
-   *
-   * @return string
-   *   Path to the feed.
-   */
-  public function getHtmlEntitiesSample() {
-    return $GLOBALS['base_url'] . '/' . drupal_get_path('module', 'aggregator') . '/tests/modules/aggregator_test/aggregator_test_title_entities.xml';
-  }
-
-  /**
-   * Creates sample article nodes.
-   *
-   * @param int $count
-   *   (optional) The number of nodes to generate. Defaults to five.
-   */
-  public function createSampleNodes($count = 5) {
-    // Post $count article nodes.
-    for ($i = 0; $i < $count; $i++) {
-      $edit = [];
-      $edit['title[0][value]'] = $this->randomMachineName();
-      $edit['body[0][value]'] = $this->randomMachineName();
-      $this->drupalPostForm('node/add/article', $edit, t('Save'));
-    }
-  }
-
-  /**
-   * Enable the plugins coming with aggregator_test module.
-   */
-  public function enableTestPlugins() {
-    $this->config('aggregator.settings')
-      ->set('fetcher', 'aggregator_test_fetcher')
-      ->set('parser', 'aggregator_test_parser')
-      ->set('processors', [
-        'aggregator_test_processor' => 'aggregator_test_processor',
-        'aggregator' => 'aggregator',
-      ])
-      ->save();
-  }
-
-}
diff --git a/core/modules/aggregator/src/Tests/AddFeedTest.php b/core/modules/aggregator/tests/src/Functional/AddFeedTest.php
similarity index 98%
rename from core/modules/aggregator/src/Tests/AddFeedTest.php
rename to core/modules/aggregator/tests/src/Functional/AddFeedTest.php
index 4dfeb95572..e4f63ea731 100644
--- a/core/modules/aggregator/src/Tests/AddFeedTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AddFeedTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
 
 /**
  * Add feed test.
diff --git a/core/modules/aggregator/src/Tests/AggregatorAdminTest.php b/core/modules/aggregator/tests/src/Functional/AggregatorAdminTest.php
similarity index 83%
rename from core/modules/aggregator/src/Tests/AggregatorAdminTest.php
rename to core/modules/aggregator/tests/src/Functional/AggregatorAdminTest.php
index 01898b6cf0..4b278d6247 100644
--- a/core/modules/aggregator/src/Tests/AggregatorAdminTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AggregatorAdminTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
 
 /**
  * Tests aggregator admin pages.
@@ -67,18 +67,22 @@ public function testOverviewPage() {
     // Check if the amount of feeds in the overview matches the amount created.
     $this->assertEqual(1, count($result), 'Created feed is found in the overview');
     // Check if the fields in the table match with what's expected.
-    $this->assertEqual($feed->label(), (string) $result[0]->td[0]->a);
+    $link = $this->xpath('//table/tbody/tr//td[1]/a');
+    $this->assertEquals($feed->label(), $link[0]->getText());
     $count = $this->container->get('entity.manager')->getStorage('aggregator_item')->getItemCount($feed);
-    $this->assertEqual(\Drupal::translation()->formatPlural($count, '1 item', '@count items'), (string) $result[0]->td[1]);
+    $td = $this->xpath('//table/tbody/tr//td[2]');
+    $this->assertEquals(\Drupal::translation()->formatPlural($count, '1 item', '@count items'), $td[0]->getText());
 
     // Update the items of the first feed.
     $feed->refreshItems();
     $this->drupalGet('admin/config/services/aggregator');
     $result = $this->xpath('//table/tbody/tr');
     // Check if the fields in the table match with what's expected.
-    $this->assertEqual($feed->label(), (string) $result[0]->td[0]->a);
+    $link = $this->xpath('//table/tbody/tr//td[1]/a');
+    $this->assertEquals($feed->label(), $link[0]->getText());
     $count = $this->container->get('entity.manager')->getStorage('aggregator_item')->getItemCount($feed);
-    $this->assertEqual(\Drupal::translation()->formatPlural($count, '1 item', '@count items'), (string) $result[0]->td[1]);
+    $td = $this->xpath('//table/tbody/tr//td[2]');
+    $this->assertEquals(\Drupal::translation()->formatPlural($count, '1 item', '@count items'), $td[0]->getText());
   }
 
 }
diff --git a/core/modules/aggregator/src/Tests/AggregatorCronTest.php b/core/modules/aggregator/tests/src/Functional/AggregatorCronTest.php
similarity index 93%
rename from core/modules/aggregator/src/Tests/AggregatorCronTest.php
rename to core/modules/aggregator/tests/src/Functional/AggregatorCronTest.php
index 9ebb2d25c0..bb7c90ae32 100644
--- a/core/modules/aggregator/src/Tests/AggregatorCronTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AggregatorCronTest.php
@@ -1,6 +1,8 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
+
+use Drupal\Tests\Traits\Core\CronRunTrait;
 
 /**
  * Update feeds on cron.
@@ -8,6 +10,9 @@
  * @group aggregator
  */
 class AggregatorCronTest extends AggregatorTestBase {
+
+  use CronRunTrait;
+
   /**
    * Adds feeds and updates them via cron process.
    */
diff --git a/core/modules/aggregator/src/Tests/AggregatorRenderingTest.php b/core/modules/aggregator/tests/src/Functional/AggregatorRenderingTest.php
similarity index 91%
rename from core/modules/aggregator/src/Tests/AggregatorRenderingTest.php
rename to core/modules/aggregator/tests/src/Functional/AggregatorRenderingTest.php
index de7e401058..37e6470847 100644
--- a/core/modules/aggregator/src/Tests/AggregatorRenderingTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AggregatorRenderingTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
 
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\views\Entity\View;
@@ -132,10 +132,14 @@ public function testFeedPage() {
 
     // Check the opml aggregator page.
     $this->drupalGet('aggregator/opml');
-    $outline = $this->xpath('//outline[1]');
-    $this->assertEqual($outline[0]['type'], 'rss', 'The correct type attribute is used for rss OPML.');
-    $this->assertEqual($outline[0]['text'], $feed->label(), 'The correct text attribute is used for rss OPML.');
-    $this->assertEqual($outline[0]['xmlurl'], $feed->getUrl(), 'The correct xmlUrl attribute is used for rss OPML.');
+    $content = $this->getSession()->getPage()->getContent();
+    // We can't use Mink xpath queries here because it only supports HTML pages,
+    // but we are dealing with XML here.
+    $xml = simplexml_load_string($content);
+    $attributes = $xml->xpath('//outline[1]')[0]->attributes();
+    $this->assertEquals('rss', $attributes->type);
+    $this->assertEquals($feed->label(), $attributes->text);
+    $this->assertEquals($feed->getUrl(), $attributes->xmlUrl);
 
     // Check for the presence of a pager.
     $this->drupalGet('aggregator/sources/' . $feed->id());
diff --git a/core/modules/aggregator/src/Tests/FeedAdminDisplayTest.php b/core/modules/aggregator/tests/src/Functional/FeedAdminDisplayTest.php
similarity index 98%
rename from core/modules/aggregator/src/Tests/FeedAdminDisplayTest.php
rename to core/modules/aggregator/tests/src/Functional/FeedAdminDisplayTest.php
index 46366b4957..e057be6e61 100644
--- a/core/modules/aggregator/src/Tests/FeedAdminDisplayTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedAdminDisplayTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
 
 /**
  * Tests the display of a feed on the Aggregator list page.
diff --git a/core/modules/aggregator/src/Tests/FeedLanguageTest.php b/core/modules/aggregator/tests/src/Functional/FeedLanguageTest.php
similarity index 95%
rename from core/modules/aggregator/src/Tests/FeedLanguageTest.php
rename to core/modules/aggregator/tests/src/Functional/FeedLanguageTest.php
index 98d04fa5c1..7e3d672c06 100644
--- a/core/modules/aggregator/src/Tests/FeedLanguageTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedLanguageTest.php
@@ -1,8 +1,9 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
 
 use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\Tests\Traits\Core\CronRunTrait;
 
 /**
  * Tests aggregator feeds in multiple languages.
@@ -11,6 +12,8 @@
  */
 class FeedLanguageTest extends AggregatorTestBase {
 
+  use CronRunTrait;
+
   /**
    * Modules to install.
    *
diff --git a/core/modules/aggregator/src/Tests/UpdateFeedItemTest.php b/core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php
similarity index 98%
rename from core/modules/aggregator/src/Tests/UpdateFeedItemTest.php
rename to core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php
index 67e96f1726..b850ca9ed8 100644
--- a/core/modules/aggregator/src/Tests/UpdateFeedItemTest.php
+++ b/core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
 use Drupal\aggregator\Entity\Feed;
 
 /**
diff --git a/core/modules/aggregator/src/Tests/UpdateFeedTest.php b/core/modules/aggregator/tests/src/Functional/UpdateFeedTest.php
similarity index 97%
rename from core/modules/aggregator/src/Tests/UpdateFeedTest.php
rename to core/modules/aggregator/tests/src/Functional/UpdateFeedTest.php
index d2308744c2..a81e0aefd1 100644
--- a/core/modules/aggregator/src/Tests/UpdateFeedTest.php
+++ b/core/modules/aggregator/tests/src/Functional/UpdateFeedTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\aggregator\Tests;
+namespace Drupal\Tests\aggregator\Functional;
 
 /**
  * Update feed test.
