diff --git a/tasks/phpstan/bootstrap.php b/tasks/phpstan/bootstrap.php
index c83c392cc4..6b4f429db1 100644
--- a/tasks/phpstan/bootstrap.php
+++ b/tasks/phpstan/bootstrap.php
@@ -4,6 +4,7 @@ define('ABSPATH', getenv('WP_ROOT') . '/');
 
 require_once ABSPATH . 'wp-load.php';
 require_once ABSPATH . 'wp-admin/includes/admin.php';
+require_once(ABSPATH . 'wp-admin/includes/ms.php');
 require_once ABSPATH . 'wp-includes/class-phpmailer.php';
 
 if (!class_exists('\MailPoet\Premium\DI\ContainerConfigurator')) {
@@ -13,3 +14,5 @@ if (!class_exists('\MailPoet\Premium\DI\ContainerConfigurator')) {
 if (!class_exists(WooCommerce::class)) {
   require_once __DIR__ . '/woocommerce.php';
 }
+
+require_once __DIR__ . '/function-stubs.php';
diff --git a/tasks/phpstan/function-stubs.php b/tasks/phpstan/function-stubs.php
new file mode 100644
index 0000000000..287d16c89f
--- /dev/null
+++ b/tasks/phpstan/function-stubs.php
@@ -0,0 +1,6 @@
+<?php
+
+if (!function_exists('members_get_cap_group')) {
+  function members_get_cap_group($name) {
+  }
+}
diff --git a/tasks/phpstan/woocommerce.php b/tasks/phpstan/woocommerce.php
index 42131e7f09..376667817c 100644
--- a/tasks/phpstan/woocommerce.php
+++ b/tasks/phpstan/woocommerce.php
@@ -73,6 +73,8 @@ class WC_Order { // phpcs:ignore
  * @method int get_product_id(string $context = 'view')
  */
 class WC_Order_Item_Product { // phpcs:ignore
+  function get_product_id() { // phpcs:ignore
+  }
 }
 
 /**
@@ -80,3 +82,13 @@ class WC_Order_Item_Product { // phpcs:ignore
  */
 class WC_Product { // phpcs:ignore
 }
+
+class WC_Cart { // phpcs:ignore
+}
+
+class WC_Mailer { // phpcs:ignore
+  function email_header() { // phpcs:ignore
+  }
+  function email_footer() { // phpcs:ignore
+  }
+}
diff --git a/tests/integration/Config/InstallerTest.php b/tests/integration/Config/InstallerTest.php
index 8622c546c7..d12a562319 100644
--- a/tests/integration/Config/InstallerTest.php
+++ b/tests/integration/Config/InstallerTest.php
@@ -32,7 +32,7 @@ class InstallerTest extends \MailPoetTest {
   }
 
   public function testItGetsPluginInformation() {
-    $args = new \StdClass;
+    $args = new \stdClass;
     $args->slug = $this->slug;
     $installer = Stub::construct(
       $this->installer,
@@ -69,11 +69,11 @@ class InstallerTest extends \MailPoetTest {
   }
 
   public function testItIgnoresNonMatchingRequestsWhenGettingPluginInformation() {
-    $data = new \StdClass;
+    $data = new \stdClass;
     $data->some_property = '123';
     $result = $this->installer->getPluginInformation($data, 'some_action', null);
     expect($result)->equals($data);
-    $args = new \StdClass;
+    $args = new \stdClass;
     $args->slug = 'different-slug';
     $result = $this->installer->getPluginInformation($data, 'plugin_information', $args);
     expect($result)->equals($data);
diff --git a/tests/integration/Config/UpdaterTest.php b/tests/integration/Config/UpdaterTest.php
index 63cdd3153e..e5a701078d 100644
--- a/tests/integration/Config/UpdaterTest.php
+++ b/tests/integration/Config/UpdaterTest.php
@@ -37,7 +37,7 @@ class UpdaterTest extends \MailPoetTest {
   }
 
   public function testItChecksForUpdates() {
-    $update_transient = new \StdClass;
+    $update_transient = new \stdClass;
     $update_transient->last_checked = time();
     $updater = Stub::construct(
       $this->updater,
@@ -75,6 +75,6 @@ class UpdaterTest extends \MailPoetTest {
 
   public function testItReturnsObjectIfPassedNonObjectWhenCheckingForUpdates() {
     $result = $this->updater->checkForUpdate(null);
-    expect($result instanceof \StdClass)->true();
+    expect($result instanceof \stdClass)->true();
   }
 }
diff --git a/tests/integration/Models/NewsletterOptionFieldTest.php b/tests/integration/Models/NewsletterOptionFieldTest.php
index 32a22d1d95..c5631a5f64 100644
--- a/tests/integration/Models/NewsletterOptionFieldTest.php
+++ b/tests/integration/Models/NewsletterOptionFieldTest.php
@@ -121,11 +121,8 @@ class NewsletterOptionFieldTest extends \MailPoetTest {
   }
 
   public function _after() {
-    ORM::forTable(NewsletterOption::$_table)
-      ->deleteMany();
-    ORM::forTable(NewsletterOptionField::$_table)
-      ->deleteMany();
-    ORM::forTable(Newsletter::$_table)
-      ->deleteMany();
+    NewsletterOption::deleteMany();
+    NewsletterOptionField::deleteMany();
+    Newsletter::deleteMany();
   }
 }
diff --git a/tests/integration/Models/NewsletterPostTest.php b/tests/integration/Models/NewsletterPostTest.php
index 0684b0e330..47daf145ab 100644
--- a/tests/integration/Models/NewsletterPostTest.php
+++ b/tests/integration/Models/NewsletterPostTest.php
@@ -22,7 +22,6 @@ class NewsletterPostTest extends \MailPoetTest {
   }
 
   public function _after() {
-    ORM::for_table(NewsletterPost::$_table)
-      ->deleteMany();
+    NewsletterPost::deleteMany();
   }
 }
diff --git a/tests/integration/Models/NewsletterTemplateTest.php b/tests/integration/Models/NewsletterTemplateTest.php
index 0e7659f2a5..674b5cc522 100644
--- a/tests/integration/Models/NewsletterTemplateTest.php
+++ b/tests/integration/Models/NewsletterTemplateTest.php
@@ -104,7 +104,6 @@ class NewsletterTemplateTest extends \MailPoetTest {
   }
 
   public function _after() {
-    ORM::for_table(NewsletterTemplate::$_table)
-      ->deleteMany();
+    NewsletterTemplate::deleteMany();
   }
 }
diff --git a/tests/integration/Models/StatisticsUnsubscribesTest.php b/tests/integration/Models/StatisticsUnsubscribesTest.php
index 3e4dc2deed..e20652d10c 100644
--- a/tests/integration/Models/StatisticsUnsubscribesTest.php
+++ b/tests/integration/Models/StatisticsUnsubscribesTest.php
@@ -27,7 +27,6 @@ class StatisticsUnsubscribesTest extends \MailPoetTest {
   }
 
   public function _after() {
-    ORM::for_table(StatisticsUnsubscribes::$_table)
-      ->deleteMany();
+    StatisticsUnsubscribes::deleteMany();
   }
 }
diff --git a/tests/integration/Models/SubscriberCustomFieldTest.php b/tests/integration/Models/SubscriberCustomFieldTest.php
index 37ffcd3cf1..043d8a241e 100644
--- a/tests/integration/Models/SubscriberCustomFieldTest.php
+++ b/tests/integration/Models/SubscriberCustomFieldTest.php
@@ -77,7 +77,6 @@ class SubscriberCustomFieldTest extends \MailPoetTest {
   }
 
   public function _after() {
-    ORM::forTable(SubscriberCustomField::$_table)
-      ->deleteMany();
+    SubscriberCustomField::deleteMany();
   }
 }
diff --git a/tests/integration/Models/SubscriberTest.php b/tests/integration/Models/SubscriberTest.php
index f97aba0fd8..d8767b346a 100644
--- a/tests/integration/Models/SubscriberTest.php
+++ b/tests/integration/Models/SubscriberTest.php
@@ -423,7 +423,7 @@ class SubscriberTest extends \MailPoetTest {
   }
 
   public function testItCanCreateOrUpdateMultipleRecords() {
-    ORM::forTable(Subscriber::$_table)->deleteMany();
+    Subscriber::deleteMany();
     $columns = [
       'first_name',
       'last_name',
diff --git a/tests/integration/Segments/WPUserWithExtraProps.php b/tests/integration/Segments/WPUserWithExtraProps.php
new file mode 100644
index 0000000000..7946df24cf
--- /dev/null
+++ b/tests/integration/Segments/WPUserWithExtraProps.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace MailPoet\Test\Segments;
+
+class WPUserWithExtraProps extends \WP_User {
+  public $order_id;
+}
diff --git a/tests/integration/Segments/WooCommerceTest.php b/tests/integration/Segments/WooCommerceTest.php
index 0fcf31454e..8ed78caa60 100644
--- a/tests/integration/Segments/WooCommerceTest.php
+++ b/tests/integration/Segments/WooCommerceTest.php
@@ -15,6 +15,8 @@ use MailPoet\Subscribers\Source;
 use MailPoetVendor\Carbon\Carbon;
 use MailPoetVendor\Idiorm\ORM;
 
+require_once('WPUserWithExtraProps.php');
+
 class WooCommerceTest extends \MailPoetTest  {
   public $customerRoleAdded;
 
@@ -585,7 +587,7 @@ class WooCommerceTest extends \MailPoetTest  {
    * Those tests are testing user synchronisation, so we need data in wp_users table which has not been synchronised to
    * mailpoet database yet. We cannot use wp_insert_user functions because they would do the sync on insert.
    *
-   * @return \WP_User
+   * @return WPUserWithExtraProps
    */
   private function insertRegisteredCustomer($number = null) {
     global $wpdb;
@@ -603,7 +605,7 @@ class WooCommerceTest extends \MailPoetTest  {
            )', $wpdb->users));
     $id = $db->lastInsertId();
     // add customer role
-    $user = new \WP_User($id);
+    $user = new WPUserWithExtraProps($id);
     $user->add_role('customer');
     $this->userEmails[] = $user->user_email;
     return $user;