diff --git a/core/modules/rdf/src/Tests/NodeAttributesTest.php b/core/modules/rdf/src/Tests/NodeAttributesTest.php
index 43f736a..417c053 100644
--- a/core/modules/rdf/src/Tests/NodeAttributesTest.php
+++ b/core/modules/rdf/src/Tests/NodeAttributesTest.php
@@ -83,14 +83,14 @@ function testNodeAttributes() {
     // Node date.
     $expected_value = array(
       'type' => 'literal',
-      'value' => date('c', $node->getCreatedTime()),
+      'value' => \Drupal::service('date.formatter')->format($node->getCreatedTime(), 'custom', 'c', 'UTC'),
       'datatype' => 'http://www.w3.org/2001/XMLSchema#dateTime',
     );
     $this->assertTrue($graph->hasProperty($node_uri, 'http://purl.org/dc/terms/date', $expected_value), 'Node date found in RDF output (dc:date).');
     // Node date.
     $expected_value = array(
       'type' => 'literal',
-      'value' => date('c', $node->getCreatedTime()),
+      'value' => \Drupal::service('date.formatter')->format($node->getCreatedTime(), 'custom', 'c', 'UTC'),
       'datatype' => 'http://www.w3.org/2001/XMLSchema#dateTime',
     );
     $this->assertTrue($graph->hasProperty($node_uri, 'http://purl.org/dc/terms/created', $expected_value), 'Node date found in RDF output (dc:created).');
diff --git a/core/modules/simpletest/src/Tests/TimeZoneTest.php b/core/modules/simpletest/src/Tests/TimeZoneTest.php
new file mode 100644
index 0000000..00c93f6
--- /dev/null
+++ b/core/modules/simpletest/src/Tests/TimeZoneTest.php
@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\simpletest\Tests\TimeZoneTest.
+ */
+
+namespace Drupal\simpletest\Tests;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * This test will check SimpleTest's default time zone handling.
+ *
+ * @group simpletest
+ */
+class TimeZoneTest extends WebTestBase {
+
+  /**
+   * A user with administrative privileges.
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->adminUser = $this->drupalCreateUser(['administer site configuration']);
+  }
+
+  /**
+   * Tests that user accounts have the default time zone set.
+   */
+  function testAccountTimeZones() {
+    $expected = 'Australia/Sydney';
+    $this->assertEqual($this->rootUser->getTimeZone(), $expected, 'Root user has correct time zone.');
+    $this->assertEqual($this->adminUser->getTimeZone(), $expected, 'Admin user has correct time zone.');
+  }
+
+}
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 2edfc81..0e1a047 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -674,6 +674,15 @@ protected function drupalLogout() {
    * being executed.
    */
   protected function setUp() {
+
+    // Set an explicit time zone to not rely on the system one, which may vary
+    // from setup to setup. The Australia/Sydney time zone is chosen so all
+    // tests are run using an edge case scenario (UTC+10 and DST). This choice
+    // is made to prevent time zone related regressions and reduce the
+    // fragility of the testing system in general. This is also set in config in
+    // \Drupal\simpletest\WebTestBase::initConfig().
+    date_default_timezone_set('Australia/Sydney');
+
     // Preserve original batch for later restoration.
     $this->setBatch();
 
@@ -983,6 +992,7 @@ protected function initUserSession() {
       'name' => 'admin',
       'mail' => 'admin@example.com',
       'pass_raw' => $this->randomMachineName(),
+      'timezone' => date_default_timezone_get(),
     ));
 
     // The child site derives its session name from the database prefix when