diff --git a/core/lib/Drupal/Core/Datetime/Element/Datelist.php b/core/lib/Drupal/Core/Datetime/Element/Datelist.php
index d3bc361..7f78fa8 100644
--- a/core/lib/Drupal/Core/Datetime/Element/Datelist.php
+++ b/core/lib/Drupal/Core/Datetime/Element/Datelist.php
@@ -6,7 +6,6 @@
 use Drupal\Core\Datetime\DateHelper;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Form\FormStateInterface;
-use DateTimeZone;
 
 /**
  * Provides a datelist element.
@@ -77,7 +76,7 @@ public static function valueCallback(&$element, $input, FormStateInterface $form
       if (!empty($element['#default_value'])) {
         $date = $element['#default_value'];
         if ($date instanceof DrupalDateTime && !$date->hasErrors()) {
-          $date->setTimezone(new DateTimeZone($element['#date_timezone']));
+          $date->setTimezone(new \DateTimeZone($element['#date_timezone']));
           static::incrementRound($date, $increment);
           foreach ($parts as $part) {
             switch ($part) {
diff --git a/core/lib/Drupal/Core/Datetime/Element/Datetime.php b/core/lib/Drupal/Core/Datetime/Element/Datetime.php
index 639dfd5..d6599ce 100644
--- a/core/lib/Drupal/Core/Datetime/Element/Datetime.php
+++ b/core/lib/Drupal/Core/Datetime/Element/Datetime.php
@@ -6,7 +6,6 @@
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Datetime\Entity\DateFormat;
-use DateTimeZone;
 
 /**
  * Provides a datetime element.
@@ -97,7 +96,7 @@ public static function valueCallback(&$element, $input, FormStateInterface $form
     else {
       $date = $element['#default_value'];
       if ($date instanceof DrupalDateTime && !$date->hasErrors()) {
-        $date->setTimezone(new DateTimeZone($element['#date_timezone']));
+        $date->setTimezone(new \DateTimeZone($element['#date_timezone']));
         $input = [
           'date'   => $date->format($element['#date_date_format']),
           'time'   => $date->format($element['#date_time_format']),
diff --git a/core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php b/core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php
index bdf2334..68cda5d 100644
--- a/core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php
@@ -2,14 +2,13 @@
 
 namespace Drupal\KernelTests\Core\Datetime\Element;
 
-use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Datetime\Entity\DateFormat;
-use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Form\FormBuilderInterface;
 use Drupal\Core\Form\FormInterface;
 use Drupal\Core\Form\FormState;
-use DateTimeZone;
-use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
 
 /**
  * Tests the timezone handling of datetime and datelist element types.
@@ -20,6 +19,7 @@
  *
  * @group Form
  */
+
 class TimezoneTest extends EntityKernelTestBase implements FormInterface {
 
   /**
@@ -128,7 +128,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     ];
 
     $dateWithwithTimeZoneA = clone $this->date;
-    $dateWithwithTimeZoneA->setTimezone(new DateTimeZone($this->timezones['zone A']));
+    $dateWithwithTimeZoneA->setTimezone(new \DateTimeZone($this->timezones['zone A']));
     $form['test6'] = [
       '#title' => 'Default date present with unusual timezone, #date_timezone same',
       '#type' => $this->elementType,
@@ -180,7 +180,7 @@ protected function setUp() {
     $this->timeFormat = DateFormat::load('html_time')->getPattern();
     $date = clone $this->date;
     foreach ($this->timezones as $label => $timezone) {
-      $date->setTimezone(new DateTimeZone($timezone));
+      $date->setTimezone(new \DateTimeZone($timezone));
       $this->formattedDates['date'][$label] = $date->format($this->dateFormat);
       $this->formattedDates['time'][$label] = $date->format($this->timeFormat);
       $this->formattedDates['day'][$label] = $date->format('j');
@@ -279,7 +279,7 @@ protected function assertTimesUnderstoodCorrectly($elementType, array $inputs) {
     $form_builder->submitForm($this, $form_state);
 
     // Examine the output of each test element.
-    $utc = new DateTimeZone('UTC');
+    $utc = new \DateTimeZone('UTC');
     $expectedDateUTC = clone $this->date;
     $expectedDateUTC->setTimezone($utc)->format('Y-m-d H:i:s');
     $wrongDates = [];
@@ -315,9 +315,9 @@ protected function assertTimesUnderstoodCorrectly($elementType, array $inputs) {
     }
 
     $message = "On all elements the time should be understood correctly as " . $expectedDateUTC . ": \n" . print_r($wrongDates, TRUE);
-    $this->assertTrue(($rightDates === $this->testConditions), $message);
+    $this->assertEquals($rightDates, $this->testConditions, $message);
     $message = "On all elements the correct timezone should be set on the value object: (expected, actual) \n" . print_r($wrongTimezones, TRUE);
-    $this->assertTrue((count($wrongTimezones) === 0), $message);
+    $this->assertCount(0, $wrongTimezones, $message);
   }
 
   /**
@@ -347,7 +347,7 @@ public function assertDateTimezonePropertyProcessed($elementType) {
         }
       }
       $this->assertEquals($this->timezones['user'], drupal_get_user_timezone(), "Subsequent tests assume specific value for drupal_get_user_timezone().");
-      $message = "The correct timezone should be set on the processed datetime elements: (expected, actual) \n" . print_r($wrongTimezones, TRUE);
+      $message = "The correct timezone should be set on the processed " . $this->elementType . " elements: (expected, actual) \n" . print_r($wrongTimezones, TRUE);
       $this->assertTrue((count($wrongTimezones) === 0), $message);
     }
   }