diff --git a/lib/API/JSON/v1/Newsletters.php b/lib/API/JSON/v1/Newsletters.php
index 7802532dfc..283f87dd51 100644
--- a/lib/API/JSON/v1/Newsletters.php
+++ b/lib/API/JSON/v1/Newsletters.php
@@ -29,6 +29,11 @@ class Newsletters extends APIEndpoint {
   public $permissions = array(
     'global' => AccessControl::PERMISSION_MANAGE_EMAILS
   );
+  private $wp;
+
+  function __construct() {
+    $this->wp = new WPFunctions;
+  }
 
   function get($data = array()) {
     $id = (isset($data['id']) ? (int)$data['id'] : false);
@@ -183,7 +188,7 @@ class Newsletters extends APIEndpoint {
       $queue = $newsletter->queue()->findOne();
       if($queue) {
         $queue->task()
-          ->whereLte('scheduled_at', Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp')))
+          ->whereLte('scheduled_at', Carbon::createFromTimestamp($this->wp->currentTime('timestamp')))
           ->where('status', SendingQueue::STATUS_SCHEDULED)
           ->findResultSet()
           ->set('scheduled_at', $next_run_date)
@@ -432,7 +437,7 @@ class Newsletters extends APIEndpoint {
       'mta_log' => Setting::getValue('mta_log'),
       'mta_method' => Setting::getValue('mta.method'),
       'cron_accessible' => CronHelper::isDaemonAccessible(),
-      'current_time' => WPFunctions::currentTime('mysql')
+      'current_time' => $this->wp->currentTime('mysql')
     ));
   }
 
diff --git a/lib/Config/Menu.php b/lib/Config/Menu.php
index ff6b9fbcd7..1af9aaf52b 100644
--- a/lib/Config/Menu.php
+++ b/lib/Config/Menu.php
@@ -38,10 +38,12 @@ class Menu {
   public $renderer;
   private $access_control;
   private $subscribers_over_limit;
+  private $wp;
 
   function __construct($renderer, AccessControl $access_control) {
     $this->renderer = $renderer;
     $this->access_control = $access_control;
+    $this->wp = new WPFunctions;
   }
 
   function init() {
@@ -372,7 +374,7 @@ class Menu {
     $data['is_old_user'] = false;
     if(!empty($data['settings']['installed_at'])) {
       $installed_at = Carbon::createFromTimestamp(strtotime($data['settings']['installed_at']));
-      $current_time = Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp'));
+      $current_time = Carbon::createFromTimestamp($this->wp->currentTime('timestamp'));
       $data['is_new_user'] = $current_time->diffInDays($installed_at) <= 30;
       $data['is_old_user'] = $current_time->diffInMonths($installed_at) >= 6;
       $data['stop_call_for_rating'] = isset($data['settings']['stop_call_for_rating']) ? $data['settings']['stop_call_for_rating'] : false;
@@ -816,7 +818,7 @@ class Menu {
       return true;
     }
     $installed_at = Carbon::createFromTimestamp(strtotime($installed_at));
-    $current_time = Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp'));
+    $current_time = Carbon::createFromTimestamp($this->wp->currentTime('timestamp'));
     return $current_time->diffInDays($installed_at) <= 30;
   }
 }
diff --git a/lib/Cron/CronHelper.php b/lib/Cron/CronHelper.php
index fe448d2097..c129ebfbb8 100644
--- a/lib/Cron/CronHelper.php
+++ b/lib/Cron/CronHelper.php
@@ -82,7 +82,8 @@ class CronHelper {
     );
     $result = self::queryCronUrl($url);
     if(is_wp_error($result)) return $result->get_error_message();
-    $response = WPFunctions::wpRemoteRetrieveBody($result);
+    $wp = new WPFunctions();
+    $response = $wp->wpRemoteRetrieveBody($result);
     $response = substr(trim($response), -strlen(DaemonHttpRunner::PING_SUCCESS_RESPONSE)) === DaemonHttpRunner::PING_SUCCESS_RESPONSE ?
       DaemonHttpRunner::PING_SUCCESS_RESPONSE :
       $response;
@@ -104,7 +105,8 @@ class CronHelper {
     $daemon['run_accessed_at'] = time();
     self::saveDaemon($daemon);
     $result = self::queryCronUrl($url);
-    return WPFunctions::wpRemoteRetrieveBody($result);
+    $wp = new WPFunctions();
+    return $wp->wpRemoteRetrieveBody($result);
   }
 
   /**
@@ -127,7 +129,7 @@ class CronHelper {
     return null;
   }
 
-  static function queryCronUrl($url) {
+  static function queryCronUrl($url, $wp = null) {
     $args = WPHooks::applyFilters(
       'mailpoet_cron_request_args',
       array(
@@ -137,7 +139,10 @@ class CronHelper {
         'user-agent' => 'MailPoet Cron'
       )
     );
-    return WPFunctions::wpRemotePost($url, $args);
+    if(is_null($wp)) {
+      $wp = new WPFunctions();
+    }
+    return $wp->wpRemotePost($url, $args);
   }
 
   static function getCronUrl($action, $data = false) {
diff --git a/lib/Cron/Workers/Scheduler.php b/lib/Cron/Workers/Scheduler.php
index 214b11a66e..0caec77cbd 100644
--- a/lib/Cron/Workers/Scheduler.php
+++ b/lib/Cron/Workers/Scheduler.php
@@ -19,6 +19,7 @@ if(!defined('ABSPATH')) exit;
 
 class Scheduler {
   public $timer;
+  private $wp;
   const UNCONFIRMED_SUBSCRIBER_RESCHEDULE_TIMEOUT = 5;
   const TASK_BATCH_SIZE = 5;
 
@@ -26,6 +27,7 @@ class Scheduler {
     $this->timer = ($timer) ? $timer : microtime(true);
     // abort if execution limit is reached
     CronHelper::enforceExecutionLimit($this->timer);
+    $this->wp = new WPFunctions();
   }
 
   function process() {
@@ -172,7 +174,7 @@ class Scheduler {
     // check if subscriber is confirmed (subscribed)
     if($subscriber->status !== Subscriber::STATUS_SUBSCRIBED) {
       // reschedule delivery in 5 minutes
-      $scheduled_at = Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp'));
+      $scheduled_at = Carbon::createFromTimestamp($this->wp->currentTime('timestamp'));
       $queue->scheduled_at = $scheduled_at->addMinutes(
         self::UNCONFIRMED_SUBSCRIBER_RESCHEDULE_TIMEOUT
       );
diff --git a/lib/Cron/Workers/SendingQueue/Migration.php b/lib/Cron/Workers/SendingQueue/Migration.php
index 61330aeb12..657debea80 100644
--- a/lib/Cron/Workers/SendingQueue/Migration.php
+++ b/lib/Cron/Workers/SendingQueue/Migration.php
@@ -241,8 +241,11 @@ class Migration extends SimpleWorker {
     return true;
   }
 
-  static function getNextRunDate() {
+  static function getNextRunDate($wp = null) {
+    if(is_null($wp)) {
+      $wp = new WPFunctions();
+    }
     // run migration immediately
-    return Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp'));
+    return Carbon::createFromTimestamp($wp->currentTime('timestamp'));
   }
 }
diff --git a/lib/Cron/Workers/SimpleWorker.php b/lib/Cron/Workers/SimpleWorker.php
index 3db2c0098b..3c637a5c73 100644
--- a/lib/Cron/Workers/SimpleWorker.php
+++ b/lib/Cron/Workers/SimpleWorker.php
@@ -11,7 +11,7 @@ if(!defined('ABSPATH')) exit;
 
 abstract class SimpleWorker {
   public $timer;
-
+  private $wp;
   const TASK_TYPE = null;
   const TASK_BATCH_SIZE = 5;
 
@@ -22,6 +22,7 @@ abstract class SimpleWorker {
     $this->timer = ($timer) ? $timer : microtime(true);
     // abort if execution limit is reached
     CronHelper::enforceExecutionLimit($this->timer);
+    $this->wp = new WPFunctions();
   }
 
   function checkProcessingRequirements() {
@@ -100,19 +101,20 @@ abstract class SimpleWorker {
   }
 
   function complete(ScheduledTask $task) {
-    $task->processed_at = WPFunctions::currentTime('mysql');
+    $task->processed_at = $this->wp->currentTime('mysql');
     $task->status = ScheduledTask::STATUS_COMPLETED;
     $task->save();
   }
 
   function reschedule(ScheduledTask $task, $timeout) {
-    $scheduled_at = Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp'));
+    $scheduled_at = Carbon::createFromTimestamp($this->wp->currentTime('timestamp'));
     $task->scheduled_at = $scheduled_at->addMinutes($timeout);
     $task->save();
   }
 
   static function getNextRunDate() {
-    $date = Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp'));
+    $wp = new WPFunctions();
+    $date = Carbon::createFromTimestamp($wp->currentTime('timestamp'));
     // Random day of the next week
     $date->setISODate($date->format('o'), $date->format('W') + 1, mt_rand(1, 7));
     $date->startOfDay();
@@ -121,8 +123,9 @@ abstract class SimpleWorker {
 
   static function getScheduledTasks($future = false) {
     $dateWhere = ($future) ? 'whereGt' : 'whereLte';
+    $wp = new WPFunctions();
     return ScheduledTask::where('type', static::TASK_TYPE)
-      ->$dateWhere('scheduled_at', Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp')))
+      ->$dateWhere('scheduled_at', Carbon::createFromTimestamp($wp->currentTime('timestamp')))
       ->whereNull('deleted_at')
       ->where('status', ScheduledTask::STATUS_SCHEDULED)
       ->limit(self::TASK_BATCH_SIZE)
@@ -130,8 +133,9 @@ abstract class SimpleWorker {
   }
 
   static function getRunningTasks() {
+    $wp = new WPFunctions();
     return ScheduledTask::where('type', static::TASK_TYPE)
-      ->whereLte('scheduled_at', Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp')))
+      ->whereLte('scheduled_at', Carbon::createFromTimestamp($wp->currentTime('timestamp')))
       ->whereNull('deleted_at')
       ->whereNull('status')
       ->limit(self::TASK_BATCH_SIZE)
diff --git a/lib/Mailer/Methods/AmazonSES.php b/lib/Mailer/Methods/AmazonSES.php
index 773a00cf8e..ef8f25e8ef 100644
--- a/lib/Mailer/Methods/AmazonSES.php
+++ b/lib/Mailer/Methods/AmazonSES.php
@@ -32,6 +32,8 @@ class AmazonSES {
   /** @var AmazonSESMapper */
   private $error_mapper;
 
+  private $wp;
+
   function __construct(
     $region,
     $access_key,
@@ -61,11 +63,12 @@ class AmazonSES {
     $this->date = gmdate('Ymd\THis\Z');
     $this->date_without_time = gmdate('Ymd');
     $this->error_mapper = $error_mapper;
+    $this->wp = new WPFunctions();
   }
 
   function send($newsletter, $subscriber, $extra_params = array()) {
     try {
-      $result = WPFunctions::wpRemotePost(
+      $result = $this->wp->wpRemotePost(
         $this->url,
         $this->request($newsletter, $subscriber, $extra_params)
       );
@@ -77,8 +80,8 @@ class AmazonSES {
       $error = $this->error_mapper->getConnectionError($result->get_error_message());
       return Mailer::formatMailerErrorResult($error);
     }
-    if(WPFunctions::wpRemoteRetrieveResponseCode($result) !== 200) {
-      $response = simplexml_load_string(WPFunctions::wpRemoteRetrieveBody($result));
+    if($this->wp->wpRemoteRetrieveResponseCode($result) !== 200) {
+      $response = simplexml_load_string($this->wp->wpRemoteRetrieveBody($result));
       $error = $this->error_mapper->getErrorFromResponse($response, $subscriber);
       return Mailer::formatMailerErrorResult($error);
     }
diff --git a/lib/Mailer/Methods/SendGrid.php b/lib/Mailer/Methods/SendGrid.php
index 67e7a518dd..b064607b4d 100644
--- a/lib/Mailer/Methods/SendGrid.php
+++ b/lib/Mailer/Methods/SendGrid.php
@@ -17,15 +17,18 @@ class SendGrid {
   /** @var SendGridMapper */
   private $error_mapper;
 
+  private $wp;
+
   function __construct($api_key, $sender, $reply_to, SendGridMapper $error_mapper) {
     $this->api_key = $api_key;
     $this->sender = $sender;
     $this->reply_to = $reply_to;
     $this->error_mapper = $error_mapper;
+    $this->wp = new WPFunctions();
   }
 
   function send($newsletter, $subscriber, $extra_params = array()) {
-    $result = WPFunctions::wpRemotePost(
+    $result = $this->wp->wpRemotePost(
       $this->url,
       $this->request($newsletter, $subscriber, $extra_params)
     );
@@ -33,7 +36,7 @@ class SendGrid {
       $error = $this->error_mapper->getConnectionError($result->get_error_message());
       return Mailer::formatMailerErrorResult($error);
     }
-    if(WPFunctions::wpRemoteRetrieveResponseCode($result) !== 200) {
+    if($this->wp->wpRemoteRetrieveResponseCode($result) !== 200) {
       $response = json_decode($result['body'], true);
       $error = $this->error_mapper->getErrorFromResponse($response, $subscriber);
       return Mailer::formatMailerErrorResult($error);
diff --git a/lib/Models/ScheduledTask.php b/lib/Models/ScheduledTask.php
index 663121193d..5b6cffcea9 100644
--- a/lib/Models/ScheduledTask.php
+++ b/lib/Models/ScheduledTask.php
@@ -16,6 +16,13 @@ class ScheduledTask extends Model {
   const PRIORITY_MEDIUM = 5;
   const PRIORITY_LOW = 10;
 
+  private $wp;
+
+  function __construct() {
+    parent::__construct();
+    $this->wp = new WPFunctions();
+  }
+
   function subscribers() {
     return $this->hasManyThrough(
       __NAMESPACE__.'\Subscriber',
@@ -61,7 +68,7 @@ class ScheduledTask extends Model {
   }
 
   function complete() {
-    $this->processed_at = WPFunctions::currentTime('mysql');
+    $this->processed_at = $this->wp->currentTime('mysql');
     $this->set('status', self::STATUS_COMPLETED);
     $this->save();
     return ($this->getErrors() === false && $this->id() > 0);
diff --git a/lib/Newsletter/Editor/PostTransformer.php b/lib/Newsletter/Editor/PostTransformer.php
index f3fb557462..40b4cef96e 100644
--- a/lib/Newsletter/Editor/PostTransformer.php
+++ b/lib/Newsletter/Editor/PostTransformer.php
@@ -14,11 +14,13 @@ class PostTransformer {
   private $args;
   private $with_layout;
   private $image_position;
+  private $wp;
 
   function __construct($args) {
     $this->args = $args;
     $this->with_layout = isset($args['withLayout']) ? (bool)filter_var($args['withLayout'], FILTER_VALIDATE_BOOLEAN) : false;
     $this->image_position = 'left';
+    $this->wp = new WPFunctions();
   }
 
   function getDivider() {
@@ -150,7 +152,7 @@ class PostTransformer {
     }
 
     $thumbnail_id = get_post_thumbnail_id($post_id);
-    $image_info = WPFunctions::getImageInfo($thumbnail_id);
+    $image_info = $this->wp->getImageInfo($thumbnail_id);
 
     // get alt text
     $alt_text = trim(strip_tags(get_post_meta(
diff --git a/lib/Newsletter/Scheduler/Scheduler.php b/lib/Newsletter/Scheduler/Scheduler.php
index edf365c89e..81b72a5b93 100644
--- a/lib/Newsletter/Scheduler/Scheduler.php
+++ b/lib/Newsletter/Scheduler/Scheduler.php
@@ -226,7 +226,8 @@ class Scheduler {
   }
 
   static function getNextRunDate($schedule, $from_timestamp = false) {
-    $from_timestamp = ($from_timestamp) ? $from_timestamp : WPFunctions::currentTime('timestamp');
+    $wp = new WPFunctions();
+    $from_timestamp = ($from_timestamp) ? $from_timestamp : $wp->currentTime('timestamp');
     try {
       $schedule = \Cron\CronExpression::factory($schedule);
       $next_run_date = $schedule->getNextRunDate(Carbon::createFromTimestamp($from_timestamp))
@@ -238,7 +239,8 @@ class Scheduler {
   }
 
   static function getPreviousRunDate($schedule, $from_timestamp = false) {
-    $from_timestamp = ($from_timestamp) ? $from_timestamp : WPFunctions::currentTime('timestamp');
+    $wp = new WPFunctions();
+    $from_timestamp = ($from_timestamp) ? $from_timestamp : $wp->currentTime('timestamp');
     try {
       $schedule = \Cron\CronExpression::factory($schedule);
       $previous_run_date = $schedule->getPreviousRunDate(Carbon::createFromTimestamp($from_timestamp))
@@ -250,7 +252,8 @@ class Scheduler {
   }
 
   static function getScheduledTimeWithDelay($after_time_type, $after_time_number) {
-    $current_time = Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp'));
+    $wp = new WPFunctions();
+    $current_time = Carbon::createFromTimestamp($wp->currentTime('timestamp'));
     switch($after_time_type) {
       case 'hours':
         return $current_time->addHours($after_time_number);
diff --git a/lib/Newsletter/Shortcodes/Categories/Date.php b/lib/Newsletter/Shortcodes/Categories/Date.php
index 350ef79573..9d535ab067 100644
--- a/lib/Newsletter/Shortcodes/Categories/Date.php
+++ b/lib/Newsletter/Shortcodes/Categories/Date.php
@@ -16,11 +16,12 @@ class Date {
       'mtext' => 'F',
       'y' => 'Y'
     );
+    $wp = new WPFunctions();
     if(!empty($action_mapping[$shortcode_details['action']])) {
-      return date_i18n($action_mapping[$shortcode_details['action']], WPFunctions::currentTime('timestamp'));
+      return date_i18n($action_mapping[$shortcode_details['action']], $wp->currentTime('timestamp'));
     }
     return ($shortcode_details['action'] === 'custom' && $shortcode_details['action_argument'] === 'format') ?
-      date_i18n($shortcode_details['action_argument_value'], WPFunctions::currentTime('timestamp')) :
+      date_i18n($shortcode_details['action_argument_value'], $wp->currentTime('timestamp')) :
       false;
   }
 }
\ No newline at end of file
diff --git a/lib/Services/Bridge.php b/lib/Services/Bridge.php
index a4989623ff..d4d3b21e02 100644
--- a/lib/Services/Bridge.php
+++ b/lib/Services/Bridge.php
@@ -56,8 +56,9 @@ class Bridge {
       'blocking' => true,
       'timeout' => 10
     );
-    $result = WPFunctions::wpRemoteGet(self::BRIDGE_URL, $params);
-    return WPFunctions::wpRemoteRetrieveResponseCode($result) === 200;
+    $wp = new WPFunctions();
+    $result = $wp->wpRemoteGet(self::BRIDGE_URL, $params);
+    return $wp->wpRemoteRetrieveResponseCode($result) === 200;
   }
 
   function initApi($api_key) {
diff --git a/lib/Services/Bridge/API.php b/lib/Services/Bridge/API.php
index 9e59961b41..6df0360d5c 100644
--- a/lib/Services/Bridge/API.php
+++ b/lib/Services/Bridge/API.php
@@ -23,6 +23,7 @@ class API {
   const RESPONSE_CODE_BANNED_ACCOUNT = 403;
 
   private $api_key;
+  private $wp;
 
   public $url_me = 'https://bridge.mailpoet.com/api/v0/me';
   public $url_premium = 'https://bridge.mailpoet.com/api/v0/premium';
@@ -30,8 +31,13 @@ class API {
   public $url_bounces = 'https://bridge.mailpoet.com/api/v0/bounces/search';
   public $url_stats = 'https://bridge.mailpoet.com/api/v0/stats';
 
-  function __construct($api_key) {
+  function __construct($api_key, $wp = null) {
     $this->setKey($api_key);
+    if(is_null($wp)) {
+      $this->wp = new WPFunctions();
+    } else {
+      $this->wp = $wp;
+    }
   }
 
   function checkMSSKey() {
@@ -40,10 +46,10 @@ class API {
       array('site' => home_url())
     );
 
-    $code = WPFunctions::wpRemoteRetrieveResponseCode($result);
+    $code = $this->wp->wpRemoteRetrieveResponseCode($result);
     switch($code) {
       case 200:
-        $body = json_decode(WPFunctions::wpRemoteRetrieveBody($result), true);
+        $body = json_decode($this->wp->wpRemoteRetrieveBody($result), true);
         break;
       default:
         $body = null;
@@ -59,10 +65,10 @@ class API {
       array('site' => home_url())
     );
 
-    $code = WPFunctions::wpRemoteRetrieveResponseCode($result);
+    $code = $this->wp->wpRemoteRetrieveResponseCode($result);
     switch($code) {
       case 200:
-        if($body = WPFunctions::wpRemoteRetrieveBody($result)) {
+        if($body = $this->wp->wpRemoteRetrieveBody($result)) {
           $body = json_decode($body, true);
         }
         break;
@@ -87,11 +93,11 @@ class API {
       );
     }
 
-    $response_code = WPFunctions::wpRemoteRetrieveResponseCode($result);
+    $response_code = $this->wp->wpRemoteRetrieveResponseCode($result);
     if($response_code !== 201) {
-      $response = (WPFunctions::wpRemoteRetrieveBody($result)) ?
-        WPFunctions::wpRemoteRetrieveBody($result) :
-        WPFunctions::wpRemoteRetrieveResponseMessage($result);
+      $response = ($this->wp->wpRemoteRetrieveBody($result)) ?
+        $this->wp->wpRemoteRetrieveBody($result) :
+        $this->wp->wpRemoteRetrieveResponseMessage($result);
       return array(
         'status' => self::SENDING_STATUS_SEND_ERROR,
         'message' => $response,
@@ -106,8 +112,8 @@ class API {
       $this->url_bounces,
       $emails
     );
-    if(WPFunctions::wpRemoteRetrieveResponseCode($result) === 200) {
-      return json_decode(WPFunctions::wpRemoteRetrieveBody($result), true);
+    if($this->wp->wpRemoteRetrieveResponseCode($result) === 200) {
+      return json_decode($this->wp->wpRemoteRetrieveBody($result), true);
     }
     return false;
   }
@@ -118,7 +124,7 @@ class API {
       array('subscriber_count' => (int)$count),
       'PUT'
     );
-    return WPFunctions::wpRemoteRetrieveResponseCode($result) === self::RESPONSE_CODE_STATS_SAVED;
+    return $this->wp->wpRemoteRetrieveResponseCode($result) === self::RESPONSE_CODE_STATS_SAVED;
   }
 
   function setKey($api_key) {
@@ -144,6 +150,6 @@ class API {
       ),
       'body' => json_encode($body)
     );
-    return WPFunctions::wpRemotePost($url, $params);
+    return $this->wp->wpRemotePost($url, $params);
   }
 }
diff --git a/lib/Services/Release/API.php b/lib/Services/Release/API.php
index ca12589a88..e8d910ff85 100644
--- a/lib/Services/Release/API.php
+++ b/lib/Services/Release/API.php
@@ -8,11 +8,12 @@ if(!defined('ABSPATH')) exit;
 
 class API {
   private $api_key;
-
+  private $wp;
   public $url_products = 'https://release.mailpoet.com/products/';
 
   function __construct($api_key) {
     $this->setKey($api_key);
+    $this->wp = new WPFunctions();
   }
 
   function getPluginInformation($plugin_name) {
@@ -20,10 +21,10 @@ class API {
       $this->url_products . $plugin_name
     );
 
-    $code = WPFunctions::wpRemoteRetrieveResponseCode($result);
+    $code = $this->wp->wpRemoteRetrieveResponseCode($result);
     switch($code) {
       case 200:
-        if($body = WPFunctions::wpRemoteRetrieveBody($result)) {
+        if($body = $this->wp->wpRemoteRetrieveBody($result)) {
           $body = json_decode($body);
         }
         break;
@@ -50,6 +51,6 @@ class API {
       'timeout' => 10,
       'httpversion' => '1.0'
     );
-    return WPFunctions::wpRemoteGet($url, $args);
+    return $this->wp->wpRemoteGet($url, $args);
   }
 }
diff --git a/lib/Tasks/Sending.php b/lib/Tasks/Sending.php
index 9d225da625..4913c8f82a 100644
--- a/lib/Tasks/Sending.php
+++ b/lib/Tasks/Sending.php
@@ -229,12 +229,13 @@ class Sending {
   }
 
   static function getScheduledQueues($amount = self::RESULT_BATCH_SIZE) {
+    $wp = new WPFunctions();
     $tasks = ScheduledTask::table_alias('tasks')
       ->select('tasks.*')
       ->join(SendingQueue::$_table, 'tasks.id = queues.task_id', 'queues')
       ->whereNull('tasks.deleted_at')
       ->where('tasks.status', ScheduledTask::STATUS_SCHEDULED)
-      ->whereLte('tasks.scheduled_at', Carbon::createFromTimestamp(WPFunctions::currentTime('timestamp')))
+      ->whereLte('tasks.scheduled_at', Carbon::createFromTimestamp($wp->currentTime('timestamp')))
       ->where('tasks.type', 'sending')
       ->whereNotEqual('tasks.status', ScheduledTask::STATUS_PAUSED)
       ->orderByAsc('tasks.updated_at')
diff --git a/lib/WP/DateTime.php b/lib/WP/DateTime.php
index 7412f86ed3..16501467c9 100644
--- a/lib/WP/DateTime.php
+++ b/lib/WP/DateTime.php
@@ -10,7 +10,10 @@ class DateTime {
   const DEFAULT_TIME_FORMAT = 'H:i:s';
   const DEFAULT_DATE_TIME_FORMAT = 'Y-m-d H:i:s';
 
+  private $wp;
+
   function __construct() {
+    $this->wp = new WPFunctions();
   }
 
   function getTimeFormat() {
@@ -27,7 +30,7 @@ class DateTime {
 
   function getCurrentTime($format=false) {
     if (empty($format)) $format = $this->getTimeFormat();
-    return WPFunctions::currentTime($format);
+    return $this->wp->currentTime($format);
   }
 
   function getCurrentDate($format=false) {
diff --git a/lib/WP/Functions.php b/lib/WP/Functions.php
index 15e2e007f4..a98c359f44 100644
--- a/lib/WP/Functions.php
+++ b/lib/WP/Functions.php
@@ -4,39 +4,31 @@ namespace MailPoet\WP;
 use MailPoet\Config\Env;
 
 class Functions {
-  static function wpRemotePost() {
-    return self::callWithFallback('wp_remote_post', func_get_args());
+  function wpRemotePost() {
+    return call_user_func_array('wp_remote_post', func_get_args());
   }
 
-  static function wpRemoteGet() {
-    return self::callWithFallback('wp_remote_get', func_get_args());
+  function wpRemoteGet() {
+    return call_user_func_array('wp_remote_get', func_get_args());
   }
 
-  static function wpRemoteRetrieveBody() {
-    return self::callWithFallback('wp_remote_retrieve_body', func_get_args());
+  function wpRemoteRetrieveBody() {
+    return call_user_func_array('wp_remote_retrieve_body', func_get_args());
   }
 
-  static function wpRemoteRetrieveResponseCode() {
-    return self::callWithFallback('wp_remote_retrieve_response_code', func_get_args());
+  function wpRemoteRetrieveResponseCode() {
+    return call_user_func_array('wp_remote_retrieve_response_code', func_get_args());
   }
 
-  static function wpRemoteRetrieveResponseMessage() {
-    return self::callWithFallback('wp_remote_retrieve_response_message', func_get_args());
+  function wpRemoteRetrieveResponseMessage() {
+    return call_user_func_array('wp_remote_retrieve_response_message', func_get_args());
   }
 
-  static function currentTime() {
-    return self::callWithFallback('current_time', func_get_args());
+  function currentTime() {
+    return call_user_func_array('current_time', func_get_args());
   }
 
-  private static function callWithFallback($func, $args) {
-    $local_func = __NAMESPACE__ . '\\' . $func;
-    if(function_exists($local_func)) {
-      return call_user_func_array($local_func, $args);
-    }
-    return call_user_func_array($func, $args);
-  }
-
-  static function getImageInfo($id) {
+  function getImageInfo($id) {
     /*
      * In some cases wp_get_attachment_image_src ignore the second parameter
      * and use global variable $content_width value instead.
diff --git a/tests/integration/Cron/CronHelperTest.php b/tests/integration/Cron/CronHelperTest.php
index e8cff41c56..e3283b16ea 100644
--- a/tests/integration/Cron/CronHelperTest.php
+++ b/tests/integration/Cron/CronHelperTest.php
@@ -2,12 +2,13 @@
 
 namespace MailPoet\Test\Cron;
 
+use Codeception\Stub;
 use AspectMock\Test as Mock;
-use Helper\WordPress as WPHelper;
 use MailPoet\Cron\CronHelper;
 use MailPoet\Cron\DaemonHttpRunner;
 use MailPoet\Models\Setting;
 use MailPoet\WP\Hooks as WPHooks;
+use MailPoet\WP\Functions as WPFunctions;
 
 class CronHelperTest extends \MailPoetTest {
   function _before() {
@@ -272,13 +273,14 @@ class CronHelperTest extends \MailPoetTest {
       expect($args)->notEmpty();
       return $request_args;
     };
-    $wp_remote_get_args = array();
-    WPHelper::interceptFunction('wp_remote_post', function() use (&$wp_remote_get_args) {
-      $wp_remote_get_args = func_get_args();
-    });
+    $wp_remote_get_args = [];
+    $wp = Stub::make(new WPFunctions(), [
+      'wpRemotePost' => function() use (&$wp_remote_get_args) {
+        return $wp_remote_get_args = func_get_args();
+      }
+    ]);
     WPHooks::addFilter('mailpoet_cron_request_args', $filter);
-
-    CronHelper::queryCronUrl('test');
+    CronHelper::queryCronUrl('test', $wp);
     expect($wp_remote_get_args[1])->equals($request_args);
 
     WPHooks::removeFilter('mailpoet_cron_request_args', $filter);
@@ -300,7 +302,6 @@ class CronHelperTest extends \MailPoetTest {
   }
 
   function _after() {
-    WPHelper::releaseAllFunctions();
     Mock::clean();
     \ORM::raw_execute('TRUNCATE ' . Setting::$_table);
   }
diff --git a/tests/integration/Cron/Workers/SendingQueue/MigrationTest.php b/tests/integration/Cron/Workers/SendingQueue/MigrationTest.php
index 351d3dab5e..08cd42c1a5 100644
--- a/tests/integration/Cron/Workers/SendingQueue/MigrationTest.php
+++ b/tests/integration/Cron/Workers/SendingQueue/MigrationTest.php
@@ -1,8 +1,9 @@
 <?php
 namespace MailPoet\Test\Cron\Workers;
 
+
 use Carbon\Carbon;
-use Helper\WordPress as WordPressHelper;
+use Codeception\Stub;
 use MailPoet\Cron\Workers\SendingQueue\Migration;
 use MailPoet\Mailer\MailerLog;
 use MailPoet\Models\ScheduledTask;
@@ -11,6 +12,7 @@ use MailPoet\Models\SendingQueue;
 use MailPoet\Models\Setting;
 use MailPoet\Models\Subscriber;
 use MailPoet\Tasks\Sending as SendingTask;
+use MailPoet\WP\Functions as WPFunctions;
 
 class MigrationTest extends \MailPoetTest {
   function _before() {
@@ -111,14 +113,15 @@ class MigrationTest extends \MailPoetTest {
   function testItUsesWPTimeToReturnNextRunDate() {
     $timestamp = 1514801410;
 
-    WordPressHelper::interceptFunction('current_time', function($time) use($timestamp) {
-      // "timestamp" string is passed as an argument
-      expect($time)->equals('timestamp');
+    $wp = Stub::make(new WPFunctions, [
+      'currentTime' => function($time) use($timestamp) {
+        // "timestamp" string is passed as an argument
+        expect($time)->equals('timestamp');
+        return $timestamp;
+      }
+    ]);
 
-      return $timestamp;
-    });
-
-    $next_run_date = Migration::getNextRunDate();
+    $next_run_date = Migration::getNextRunDate($wp);
     expect($next_run_date->timestamp)->equals($timestamp);
   }
 
@@ -200,7 +203,5 @@ class MigrationTest extends \MailPoetTest {
       $this->restoreTable();
       $this->altered = false;
     }
-
-    WordPressHelper::releaseAllFunctions();
   }
 }
diff --git a/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php b/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php
index a7be15e031..ade2db8204 100644
--- a/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php
+++ b/tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php
@@ -231,8 +231,9 @@ class NewsletterTest extends \MailPoetTest {
     $queue = $this->queue;
     $newsletter = $this->newsletter_task->preProcessNewsletter($newsletter, $queue);
     $queue = SendingTask::getByNewsletterId($newsletter->id);
+    $wp = new Functions();
     expect($queue->newsletter_rendered_subject)
-      ->contains(date_i18n('dS', Functions::currentTime('timestamp')));
+      ->contains(date_i18n('dS', $wp->currentTime('timestamp')));
   }
 
 
diff --git a/tests/integration/Services/BridgeTest.php b/tests/integration/Services/BridgeTest.php
index 68a4f20b05..64a7d8cb77 100644
--- a/tests/integration/Services/BridgeTest.php
+++ b/tests/integration/Services/BridgeTest.php
@@ -3,13 +3,13 @@
 namespace MailPoet\Test\Services;
 
 use Codeception\Util\Stub;
-use Helper\WordPress as WPHelper;
 use MailPoet\Mailer\Mailer;
 use MailPoet\Models\Setting;
 use MailPoet\Services\Bridge;
 use MailPoet\Services\Bridge\API;
 use MailPoet\Services\Bridge\BridgeTestMockAPI as MockAPI;
 use MailPoet\WP\Hooks as WPHooks;
+use MailPoet\WP\Functions as WPFunctions;
 
 require_once('BridgeTestMockAPI.php');
 
@@ -257,10 +257,12 @@ class BridgeTest extends \MailPoetTest {
 
   function testItAllowsChangingRequestTimeout() {
     $wp_remote_post_args = array();
-    WPHelper::interceptFunction('wp_remote_post', function() use (&$wp_remote_post_args) {
-      $wp_remote_post_args = func_get_args();
-    });
-    $api = new API('test_key');
+    $wp = Stub::make(new WPFunctions, [
+      'wpRemotePost' => function() use (&$wp_remote_post_args) {
+        $wp_remote_post_args = func_get_args();
+      }
+    ]);
+    $api = new API('test_key', $wp);
 
     // test default request value
     $api->sendMessages('test');
@@ -311,7 +313,6 @@ class BridgeTest extends \MailPoetTest {
   }
 
   function _after() {
-    WPHelper::releaseAllFunctions();
     \ORM::raw_execute('TRUNCATE ' . Setting::$_table);
   }
 }
diff --git a/tests/integration/WP/FunctionsTest.php b/tests/integration/WP/FunctionsTest.php
index 684360674e..440446111a 100644
--- a/tests/integration/WP/FunctionsTest.php
+++ b/tests/integration/WP/FunctionsTest.php
@@ -50,7 +50,8 @@ class FunctionsTest extends \MailPoetTest {
     $id = $this->makeAttachment($upload);
     expect($id)->notEmpty();
 
-    $image = WPFunctions::getImageInfo($id);
+    $wp = new WPFunctions();
+    $image = $wp->getImageInfo($id);
     expect($image[1])->equals(Env::NEWSLETTER_CONTENT_WIDTH);
 
     wp_delete_attachment($id, $force_delete = true);