diff --git a/mailpoet/lib/API/API.php b/mailpoet/lib/API/API.php
index d07fed0c9c..ff2c7ff884 100644
--- a/mailpoet/lib/API/API.php
+++ b/mailpoet/lib/API/API.php
@@ -12,6 +12,7 @@ class API {
    * @throws \Exception
    */
   public static function MP($version) {
+    /** @var class-string<\MailPoet\API\MP\v1\API> $apiClass */
     $apiClass = sprintf('%s\MP\%s\API', __NAMESPACE__, $version);
     try {
       return ContainerWrapper::getInstance()->get($apiClass);
diff --git a/mailpoet/lib/DI/ContainerWrapper.php b/mailpoet/lib/DI/ContainerWrapper.php
index a161a1c694..643cd50ffc 100644
--- a/mailpoet/lib/DI/ContainerWrapper.php
+++ b/mailpoet/lib/DI/ContainerWrapper.php
@@ -64,7 +64,7 @@ class ContainerWrapper implements ContainerInterface {
     return $this->premiumContainer;
   }
 
-  public static function getInstance($debug = false) {
+  public static function getInstance($debug = false): ContainerWrapper {
     if (self::$instance) {
       return self::$instance;
     }
diff --git a/mailpoet/lib/Subscribers/ImportExport/PersonalDataExporters/NewsletterStatsBaseExporter.php b/mailpoet/lib/Subscribers/ImportExport/PersonalDataExporters/NewsletterStatsBaseExporter.php
index 65220a4985..160bdf3ef9 100644
--- a/mailpoet/lib/Subscribers/ImportExport/PersonalDataExporters/NewsletterStatsBaseExporter.php
+++ b/mailpoet/lib/Subscribers/ImportExport/PersonalDataExporters/NewsletterStatsBaseExporter.php
@@ -4,12 +4,15 @@ namespace MailPoet\Subscribers\ImportExport\PersonalDataExporters;
 
 use MailPoet\DI\ContainerWrapper;
 use MailPoet\Entities\SubscriberEntity;
+use MailPoet\Statistics\StatisticsClicksRepository;
+use MailPoet\Statistics\StatisticsOpensRepository;
 use MailPoet\Subscribers\SubscribersRepository;
 
 abstract class NewsletterStatsBaseExporter {
 
   const LIMIT = 100;
 
+  /** @var class-string<StatisticsClicksRepository>|class-string<StatisticsOpensRepository> */
   protected $statsClassName;
 
   protected $subscriberRepository;
@@ -38,6 +41,8 @@ abstract class NewsletterStatsBaseExporter {
     $result = [];
 
     $statsClass = ContainerWrapper::getInstance()->get($this->statsClassName);
+
+    /** @var array[] $statistics */
     $statistics = $statsClass->getAllForSubscriber($subscriber)
       ->setMaxResults(self::LIMIT)
       ->setFirstResult(self::LIMIT * ($page - 1))
diff --git a/mailpoet/lib/Tasks/Sending.php b/mailpoet/lib/Tasks/Sending.php
index 8d8da6e3df..3e872ab69c 100644
--- a/mailpoet/lib/Tasks/Sending.php
+++ b/mailpoet/lib/Tasks/Sending.php
@@ -5,6 +5,7 @@ namespace MailPoet\Tasks;
 use MailPoet\Cron\Workers\SendingQueue\SendingQueue as SendingQueueAlias;
 use MailPoet\DI\ContainerWrapper;
 use MailPoet\Entities\SendingQueueEntity;
+use MailPoet\InvalidStateException;
 use MailPoet\Logging\LoggerFactory;
 use MailPoet\Models\ScheduledTask;
 use MailPoet\Models\ScheduledTaskSubscriber;
@@ -194,6 +195,9 @@ class Sending {
   public function getSendingQueueEntity(): SendingQueueEntity {
     $sendingQueuesRepository = ContainerWrapper::getInstance()->get(SendingQueuesRepository::class);
     $sendingQueueEntity = $sendingQueuesRepository->findOneById($this->queue->id);
+    if (!$sendingQueueEntity) {
+      throw new InvalidStateException();
+    }
     $sendingQueuesRepository->refresh($sendingQueueEntity);
 
     return $sendingQueueEntity;
diff --git a/mailpoet/tests/DataFactories/AutomationRun.php b/mailpoet/tests/DataFactories/AutomationRun.php
index abb4c00290..bd46c704e5 100644
--- a/mailpoet/tests/DataFactories/AutomationRun.php
+++ b/mailpoet/tests/DataFactories/AutomationRun.php
@@ -13,6 +13,7 @@ use MailPoet\Automation\Engine\Storage\AutomationRunLogStorage;
 use MailPoet\Automation\Engine\Storage\AutomationRunStorage;
 use MailPoet\Automation\Engine\Storage\AutomationStorage;
 use MailPoet\DI\ContainerWrapper;
+use MailPoet\InvalidStateException;
 
 class AutomationRun {
 
@@ -106,11 +107,17 @@ class AutomationRun {
     $id = $this->storage->createAutomationRun($automationRun);
     $this->storage->updateNextStep($id, $this->nextStep);
     $this->automationRun = $this->storage->getAutomationRun($id);
+    if (!$this->automationRun) {
+      throw new InvalidStateException();
+    }
     return $this->automationRun;
   }
 
   public function generateLogs(Entity $run, string $lastStep) {
     $automation = ContainerWrapper::getInstance(WP_DEBUG)->get(AutomationStorage::class)->getAutomation($run->getAutomationId());
+    if (!$automation) {
+      throw new InvalidStateException();
+    }
     $steps = $this->findPathToStep($automation, $lastStep);
 
     $logStorage = ContainerWrapper::getInstance(WP_DEBUG)->get(AutomationRunLogStorage::class);
diff --git a/mailpoet/tests/_support/IntegrationCleanupExtension.php b/mailpoet/tests/_support/IntegrationCleanupExtension.php
index 32e87cac17..69080e45ac 100644
--- a/mailpoet/tests/_support/IntegrationCleanupExtension.php
+++ b/mailpoet/tests/_support/IntegrationCleanupExtension.php
@@ -27,6 +27,8 @@ class IntegrationCleanupExtension extends Extension {
     $this->entityManager = ContainerWrapper::getInstance()->get(EntityManager::class);
 
     $mpPrefix = Env::$dbPrefix;
+
+    /** @var string[] $tables */
     $tables = $this->entityManager->getConnection()->fetchFirstColumn("
       SELECT table_name
       FROM information_schema.tables
diff --git a/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php b/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php
index f34542ff54..ed04d41899 100644
--- a/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php
+++ b/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php
@@ -250,6 +250,7 @@ class NewsletterTest extends \MailPoetTest {
     $newsletterPost = $newsletterPostRepository->findOneBy(['newsletter' => $this->newsletter->getId()]);
     expect($newsletterPost)->isInstanceOf(NewsletterPostEntity::class);
     expect($result)->notEquals(false);
+    $this->assertInstanceOf(NewsletterPostEntity::class, $newsletterPost);
     expect($newsletterPost->getPostId())->equals('10');
   }
 
diff --git a/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/PostsTest.php b/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/PostsTest.php
index 516e6518ad..d40ae176e4 100644
--- a/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/PostsTest.php
+++ b/mailpoet/tests/integration/Cron/Workers/SendingQueue/Tasks/PostsTest.php
@@ -47,8 +47,8 @@ class PostsTest extends \MailPoetTest {
     expect($this->postsTask->extractAndSave($renderedNewsletter, $newsletter))->equals(true);
     $newsletterPostRepository = ContainerWrapper::getInstance()->get(NewsletterPostsRepository::class);
     $newsletterPost = $newsletterPostRepository->findOneBy(['newsletter' => $parent]);
-    expect($newsletterPost)->isInstanceOf(NewsletterPostEntity::class);
-    expect($newsletterPost->getPostId())->equals($postId);
+    $this->assertInstanceOf(NewsletterPostEntity::class, $newsletterPost);
+    $this->assertSame($newsletterPost->getPostId(), $postId);
   }
 
   public function testItDoesNotSavePostsWhenNewsletterIsNotANotificationHistory() {
diff --git a/mailpoet/tests/integration/REST/Automation/Automations/AutomationsCreateFromTemplateTest.php b/mailpoet/tests/integration/REST/Automation/Automations/AutomationsCreateFromTemplateTest.php
index 93fd48e208..4bb97876c5 100644
--- a/mailpoet/tests/integration/REST/Automation/Automations/AutomationsCreateFromTemplateTest.php
+++ b/mailpoet/tests/integration/REST/Automation/Automations/AutomationsCreateFromTemplateTest.php
@@ -72,7 +72,8 @@ class AutomationsCreateFromTemplateTest extends AutomationTest {
     ]);
     $allAutomations = $storage->getAutomations();
     $createdAutomation = array_pop($allAutomations);
-    expect($createdAutomation->getStatus())->equals('draft');
+    $this->assertInstanceOf(Automation::class, $createdAutomation);
+    $this->assertSame($createdAutomation->getStatus(), 'draft');
   }
 
   public function testAutomationsCreatedFromTemplatesReturnsAutomationId(): void {