diff --git a/core/modules/system/src/Tests/Common/FormatDateTest.php b/core/modules/system/src/Tests/Common/FormatDateTest.php
index 36589ef..cddf0a3 100644
--- a/core/modules/system/src/Tests/Common/FormatDateTest.php
+++ b/core/modules/system/src/Tests/Common/FormatDateTest.php
@@ -77,46 +77,4 @@ function testAdminDefinedFormatDate() {
     $this->assertIdentical(format_date($timestamp, 'undefined_style'), format_date($timestamp, 'fallback'), 'Test format_date() defaulting to `fallback` when $type not found.');
   }
 
-  /**
-   * Tests the format_date() function.
-   */
-  function testFormatDate() {
-    $timestamp = strtotime('2007-03-26T00:00:00+00:00');
-    $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'America/Los_Angeles', 'en'), 'Sunday, 25-Mar-07 17:00:00 PDT', 'Test all parameters.');
-    $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), 'domingo, 25-Mar-07 17:00:00 PDT', 'Test translated format.');
-    $this->assertIdentical(format_date($timestamp, 'custom', '\\l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), 'l, 25-Mar-07 17:00:00 PDT', 'Test an escaped format string.');
-    $this->assertIdentical(format_date($timestamp, 'custom', '\\\\l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), '\\domingo, 25-Mar-07 17:00:00 PDT', 'Test format containing backslash character.');
-    $this->assertIdentical(format_date($timestamp, 'custom', '\\\\\\l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), '\\l, 25-Mar-07 17:00:00 PDT', 'Test format containing backslash followed by escaped format string.');
-    $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'Europe/London', 'en'), 'Monday, 26-Mar-07 01:00:00 BST', 'Test a different time zone.');
-
-    // Change the default language and timezone.
-    $this->config('system.site')->set('default_langcode', static::LANGCODE)->save();
-    date_default_timezone_set('America/Los_Angeles');
-
-    // Reset the language manager so new negotiations attempts will fall back on
-    // on the new language.
-    $this->container->get('language_manager')->reset();
-
-    $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'America/Los_Angeles', 'en'), 'Sunday, 25-Mar-07 17:00:00 PDT', 'Test a different language.');
-    $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'Europe/London'), 'Monday, 26-Mar-07 01:00:00 BST', 'Test a different time zone.');
-    $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T'), 'domingo, 25-Mar-07 17:00:00 PDT', 'Test custom date format.');
-    $this->assertIdentical(format_date($timestamp, 'long'), 'domingo, 25. marzo 2007 - 17:00', 'Test long date format.');
-    $this->assertIdentical(format_date($timestamp, 'medium'), '25. marzo 2007 - 17:00', 'Test medium date format.');
-    $this->assertIdentical(format_date($timestamp, 'short'), '2007 Mar 25 - 5:00pm', 'Test short date format.');
-    $this->assertIdentical(format_date($timestamp), '25. marzo 2007 - 17:00', 'Test default date format.');
-    // Test HTML time element formats.
-    $this->assertIdentical(format_date($timestamp, 'html_datetime'), '2007-03-25T17:00:00-0700', 'Test html_datetime date format.');
-    $this->assertIdentical(format_date($timestamp, 'html_date'), '2007-03-25', 'Test html_date date format.');
-    $this->assertIdentical(format_date($timestamp, 'html_time'), '17:00:00', 'Test html_time date format.');
-    $this->assertIdentical(format_date($timestamp, 'html_yearless_date'), '03-25', 'Test html_yearless_date date format.');
-    $this->assertIdentical(format_date($timestamp, 'html_week'), '2007-W12', 'Test html_week date format.');
-    $this->assertIdentical(format_date($timestamp, 'html_month'), '2007-03', 'Test html_month date format.');
-    $this->assertIdentical(format_date($timestamp, 'html_year'), '2007', 'Test html_year date format.');
-
-    // HTML is not escaped by the date formatter, it must be escaped later.
-    $formatter = \Drupal::service('date.formatter');
-    $this->assertIdentical($formatter->format($timestamp, 'custom', '\<\s\c\r\i\p\t\>\a\l\e\r\t\(\'Y\'\)\;\<\/\s\c\r\i\p\t\>'), "<script>alert('2007');</script>", 'Script tags not removed from dates.');
-    $this->assertIdentical($formatter->format($timestamp, 'custom', '\<\e\m\>Y\<\/\e\m\>'), '<em>2007</em>', 'Em tags are not removed from dates.');
-  }
-
 }
diff --git a/core/tests/Drupal/KernelTests/Core/Datetime/FormatDateTest.php b/core/tests/Drupal/KernelTests/Core/Datetime/FormatDateTest.php
new file mode 100644
index 0000000..893b11e
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Datetime/FormatDateTest.php
@@ -0,0 +1,90 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Datetime;
+
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\language\Entity\ConfigurableLanguage;
+
+/**
+ * Tests date formatting.
+ *
+ * @group Common
+ */
+class FormatDateTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['language', 'system'];
+
+  /**
+   * Arbitrary langcode for a custom language.
+   */
+  const LANGCODE = 'xx';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installConfig(['system']);
+
+    $this->setSetting('locale_custom_strings_' . self::LANGCODE, [
+      '' => array('Sunday' => 'domingo'),
+      'Long month name' => array('March' => 'marzo'),
+    ]);
+
+    $formats = $this->container->get('entity.manager')
+      ->getStorage('date_format')
+      ->loadMultiple(['long', 'medium', 'short']);
+    $formats['long']->setPattern('l, j. F Y - G:i')->save();
+    $formats['medium']->setPattern('j. F Y - G:i')->save();
+    $formats['short']->setPattern('Y M j - g:ia')->save();
+
+    ConfigurableLanguage::createFromLangcode(static::LANGCODE)->save();
+  }
+
+  /**
+   * Tests the format_date() function.
+   */
+  function testFormatDate() {
+    $timestamp = strtotime('2007-03-26T00:00:00+00:00');
+    $this->assertSame(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'America/Los_Angeles', 'en'), 'Sunday, 25-Mar-07 17:00:00 PDT', 'Test all parameters.');
+    $this->assertSame(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), 'domingo, 25-Mar-07 17:00:00 PDT', 'Test translated format.');
+    $this->assertSame(format_date($timestamp, 'custom', '\\l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), 'l, 25-Mar-07 17:00:00 PDT', 'Test an escaped format string.');
+    $this->assertSame(format_date($timestamp, 'custom', '\\\\l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), '\\domingo, 25-Mar-07 17:00:00 PDT', 'Test format containing backslash character.');
+    $this->assertSame(format_date($timestamp, 'custom', '\\\\\\l, d-M-y H:i:s T', 'America/Los_Angeles', self::LANGCODE), '\\l, 25-Mar-07 17:00:00 PDT', 'Test format containing backslash followed by escaped format string.');
+    $this->assertSame(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'Europe/London', 'en'), 'Monday, 26-Mar-07 01:00:00 BST', 'Test a different time zone.');
+
+    // Change the default language and timezone.
+    $this->config('system.site')->set('default_langcode', static::LANGCODE)->save();
+    date_default_timezone_set('America/Los_Angeles');
+
+    // Reset the language manager so new negotiations attempts will fall back on
+    // on the new language.
+    $this->container->get('language_manager')->reset();
+
+    $this->assertSame(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'America/Los_Angeles', 'en'), 'Sunday, 25-Mar-07 17:00:00 PDT', 'Test a different language.');
+    $this->assertSame(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'Europe/London'), 'Monday, 26-Mar-07 01:00:00 BST', 'Test a different time zone.');
+    $this->assertSame(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T'), 'domingo, 25-Mar-07 17:00:00 PDT', 'Test custom date format.');
+    $this->assertSame(format_date($timestamp, 'long'), 'domingo, 25. marzo 2007 - 17:00', 'Test long date format.');
+    $this->assertSame(format_date($timestamp, 'medium'), '25. marzo 2007 - 17:00', 'Test medium date format.');
+    $this->assertSame(format_date($timestamp, 'short'), '2007 Mar 25 - 5:00pm', 'Test short date format.');
+    $this->assertSame(format_date($timestamp), '25. marzo 2007 - 17:00', 'Test default date format.');
+    // Test HTML time element formats.
+    $this->assertSame(format_date($timestamp, 'html_datetime'), '2007-03-25T17:00:00-0700', 'Test html_datetime date format.');
+    $this->assertSame(format_date($timestamp, 'html_date'), '2007-03-25', 'Test html_date date format.');
+    $this->assertSame(format_date($timestamp, 'html_time'), '17:00:00', 'Test html_time date format.');
+    $this->assertSame(format_date($timestamp, 'html_yearless_date'), '03-25', 'Test html_yearless_date date format.');
+    $this->assertSame(format_date($timestamp, 'html_week'), '2007-W12', 'Test html_week date format.');
+    $this->assertSame(format_date($timestamp, 'html_month'), '2007-03', 'Test html_month date format.');
+    $this->assertSame(format_date($timestamp, 'html_year'), '2007', 'Test html_year date format.');
+
+    // HTML is not escaped by the date formatter, it must be escaped later.
+    $formatter = $this->container->get('date.formatter');
+    $this->assertSame($formatter->format($timestamp, 'custom', '\<\s\c\r\i\p\t\>\a\l\e\r\t\(\'Y\'\)\;\<\/\s\c\r\i\p\t\>'), "<script>alert('2007');</script>", 'Script tags not removed from dates.');
+    $this->assertSame($formatter->format($timestamp, 'custom', '\<\e\m\>Y\<\/\e\m\>'), '<em>2007</em>', 'Em tags are not removed from dates.');
+  }
+
+}