diff --git a/tests/integration/Newsletter/Links/LinksTest.php b/tests/integration/Newsletter/Links/LinksTest.php
index b3d1ec1af7..5b6c1bee83 100644
--- a/tests/integration/Newsletter/Links/LinksTest.php
+++ b/tests/integration/Newsletter/Links/LinksTest.php
@@ -186,6 +186,7 @@ class LinksTest extends \MailPoetTest {
     $newsltterLink = NewsletterLink::where('newsletter_id', 1)
       ->where('queue_id', 1)
       ->findOne();
+    assert($newsltterLink instanceof NewsletterLink);
     expect($newsltterLink->hash)->equals('123');
     expect($newsltterLink->url)->equals('http://example.com');
   }
diff --git a/tests/integration/Newsletter/Scheduler/AutomaticEmailTest.php b/tests/integration/Newsletter/Scheduler/AutomaticEmailTest.php
index f4e98e6df9..54a52aaf4a 100644
--- a/tests/integration/Newsletter/Scheduler/AutomaticEmailTest.php
+++ b/tests/integration/Newsletter/Scheduler/AutomaticEmailTest.php
@@ -37,6 +37,7 @@ class AutomaticEmailTest extends \MailPoetTest {
       ]
     );
     $newsletter = Newsletter::filter('filterWithOptions', Newsletter::TYPE_AUTOMATIC)->findOne($newsletter->id);
+    assert($newsletter instanceof Newsletter);
     $subscriber = Subscriber::create();
     $subscriber->hydrate(Fixtures::get('subscriber_template'));
     $subscriber->save();
@@ -68,6 +69,7 @@ class AutomaticEmailTest extends \MailPoetTest {
       ]
     );
     $newsletter = Newsletter::filter('filterWithOptions', Newsletter::TYPE_AUTOMATIC)->findOne($newsletter->id);
+    assert($newsletter instanceof Newsletter);
     $subscriber = Subscriber::create();
     $subscriber->hydrate(Fixtures::get('subscriber_template'));
     $subscriber->save();
@@ -76,6 +78,7 @@ class AutomaticEmailTest extends \MailPoetTest {
     $this->automaticEmailScheduler->createAutomaticEmailSendingTask($newsletter, $subscriber->id, $meta);
     // new queue record should be created with meta data
     $queue = SendingQueue::where('newsletter_id', $newsletter->id)->findOne();
+    assert($queue instanceof SendingQueue);
     expect($queue->getMeta())->equals($meta);
   }
 
@@ -90,6 +93,7 @@ class AutomaticEmailTest extends \MailPoetTest {
       ]
     );
     $newsletter = Newsletter::filter('filterWithOptions', Newsletter::TYPE_AUTOMATIC)->findOne($newsletter->id);
+    assert($newsletter instanceof Newsletter);
 
     $this->automaticEmailScheduler->createAutomaticEmailSendingTask($newsletter, $subscriber = null, $meta = null);
     // new scheduled task should be created
diff --git a/tests/integration/Newsletter/ShortcodesTest.php b/tests/integration/Newsletter/ShortcodesTest.php
index ca04953b4c..fa4ccf3418 100644
--- a/tests/integration/Newsletter/ShortcodesTest.php
+++ b/tests/integration/Newsletter/ShortcodesTest.php
@@ -18,6 +18,7 @@ use MailPoet\Settings\SettingsController;
 use MailPoet\Subscribers\LinkTokens;
 use MailPoet\Subscription\SubscriptionUrlFactory;
 use MailPoet\WP\Functions as WPFunctions;
+use WP_Post;
 
 require_once(ABSPATH . 'wp-admin/includes/user.php');
 
@@ -136,6 +137,7 @@ class ShortcodesTest extends \MailPoetTest {
     $result =
       $shortcodesObject->process(['[newsletter:post_title]'], $content);
     $wpPost = get_post($this->wPPost);
+    assert($wpPost instanceof WP_Post);
     expect($result['0'])->equals($wpPost->post_title); // phpcs:ignore Squiz.NamingConventions.ValidVariableName.NotCamelCaps
   }