diff --git a/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
index 317f64e..c71097c 100644
--- a/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -19,6 +19,9 @@
 use Drupal\Core\StreamWrapper\StreamWrapperInterface;
 use Drupal\Core\Test\TestRunnerKernel;
 use Drupal\Core\Url;
+use Drupal\Tests\RandomGeneratorTrait;
+use Drupal\Tests\SessionTestTrait;
+use Drupal\Tests\WebAssert as WebAssertClass;
 use Drupal\user\Entity\Role;
 use Drupal\user\Entity\User;
 use Drupal\user\UserInterface;
@@ -466,11 +469,11 @@ public function getSession($name = NULL) {
    * @param string $name
    *   (optional) Name of the session. Defaults to the active session.
    *
-   * @return \Drupal\simpletest\WebAssert
+   * @return \Drupal\Tests\WebAssert
    *   A new web-assert option for asserting the presence of elements with.
    */
   public function assertSession($name = NULL) {
-    return new WebAssert($this->getSession($name));
+    return new WebAssertClass($this->getSession($name));
   }
 
   /**
diff --git a/core/modules/simpletest/src/RandomGeneratorTrait.php b/core/modules/simpletest/src/RandomGeneratorTrait.php
index 2d8b635..be7fa0e 100644
--- a/core/modules/simpletest/src/RandomGeneratorTrait.php
+++ b/core/modules/simpletest/src/RandomGeneratorTrait.php
@@ -6,6 +6,11 @@
 
 /**
  * Provides random generator utility methods.
+ *
+ * @deprecated in Drupal 8.0.0, will be removed before Drupal 9.0.0.
+ * The trait was moved to another namespace.
+ *
+ * @see \Drupal\Tests
  */
 trait RandomGeneratorTrait {
 
diff --git a/core/modules/simpletest/src/SessionTestTrait.php b/core/modules/simpletest/src/SessionTestTrait.php
index 042956e..f041614 100644
--- a/core/modules/simpletest/src/SessionTestTrait.php
+++ b/core/modules/simpletest/src/SessionTestTrait.php
@@ -6,6 +6,11 @@
 
 /**
  * Provides methods to generate and get session name in tests.
+ *
+ * @deprecated in Drupal 8.0.0 will be removed before 9.0.0.
+ * This was moved to another namespace.
+ *
+ * @see \Drupal\Tests
  */
 trait SessionTestTrait {
 
diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index 03d308d..54223f5 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\simpletest;
 
+use Behat\Mink\Session;
 use Drupal\Component\Render\MarkupInterface;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\SafeMarkup;
@@ -13,6 +14,8 @@
 use Drupal\Core\Site\Settings;
 use Drupal\Core\StreamWrapper\PublicStream;
 use Drupal\Core\Utility\Error;
+use Drupal\Tests\RandomGeneratorTrait;
+use Drupal\Tests\SessionTestTrait;
 
 /**
  * Base class for Drupal tests.
diff --git a/core/modules/simpletest/src/WebAssert.php b/core/modules/simpletest/src/WebAssert.php
index 063473b..56f4465 100644
--- a/core/modules/simpletest/src/WebAssert.php
+++ b/core/modules/simpletest/src/WebAssert.php
@@ -8,6 +8,11 @@
 
 /**
  * Defines a class with methods for asserting presence of elements during tests.
+ *
+ * @deprecated in Drupal 8.0.0 will be removed before 9.0.0.
+ * This was moved to another namespace.
+ *
+ * @see \Drupal\Tests
  */
 class WebAssert extends MinkWebAssert {
 
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index dffe81d..7e50430 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -19,7 +19,7 @@
 use Drupal\Core\Site\Settings;
 use Drupal\simpletest\AssertContentTrait;
 use Drupal\simpletest\AssertHelperTrait;
-use Drupal\simpletest\RandomGeneratorTrait;
+use Drupal\Tests\RandomGeneratorTrait;
 use Drupal\simpletest\TestServiceProvider;
 use Symfony\Component\DependencyInjection\Reference;
 use Symfony\Component\HttpFoundation\Request;
diff --git a/core/tests/Drupal/Tests/RandomGeneratorTrait.php b/core/tests/Drupal/Tests/RandomGeneratorTrait.php
new file mode 100644
index 0000000..4fdd89a
--- /dev/null
+++ b/core/tests/Drupal/Tests/RandomGeneratorTrait.php
@@ -0,0 +1,126 @@
+<?php
+
+namespace Drupal\Tests;
+
+use Drupal\Component\Utility\Random;
+
+/**
+ * Provides random generator utility methods.
+ */
+trait RandomGeneratorTrait {
+
+  /**
+   * The random generator.
+   *
+   * @var \Drupal\Component\Utility\Random
+   */
+  protected $randomGenerator;
+
+  /**
+   * Generates a pseudo-random string of ASCII characters of codes 32 to 126.
+   *
+   * Do not use this method when special characters are not possible (e.g., in
+   * machine or file names that have already been validated); instead, use
+   * \Drupal\simpletest\TestBase::randomMachineName(). If $length is greater
+   * than 3 the random string will include at least one ampersand ('&') and
+   * at least one greater than ('>') character to ensure coverage for special
+   * characters and avoid the introduction of random test failures.
+   *
+   * @param int $length
+   *   Length of random string to generate.
+   *
+   * @return string
+   *   Pseudo-randomly generated unique string including special characters.
+   *
+   * @see \Drupal\Component\Utility\Random::string()
+   */
+  public function randomString($length = 8) {
+    if ($length < 4) {
+      return $this->getRandomGenerator()->string($length, TRUE, array($this, 'randomStringValidate'));
+    }
+
+    // To prevent the introduction of random test failures, ensure that the
+    // returned string contains a character that needs to be escaped in HTML by
+    // injecting an ampersand into it.
+    $replacement_pos = floor($length / 2);
+    // Remove 2 from the length to account for the ampersand and greater than
+    // characters.
+    $string = $this->getRandomGenerator()->string($length - 2, TRUE, array($this, 'randomStringValidate'));
+    return substr_replace($string, '>&', $replacement_pos, 0);
+  }
+
+  /**
+   * Callback for random string validation.
+   *
+   * @see \Drupal\Component\Utility\Random::string()
+   *
+   * @param string $string
+   *   The random string to validate.
+   *
+   * @return bool
+   *   TRUE if the random string is valid, FALSE if not.
+   */
+  public function randomStringValidate($string) {
+    // Consecutive spaces causes issues for
+    // \Drupal\simpletest\WebTestBase::assertLink().
+    if (preg_match('/\s{2,}/', $string)) {
+      return FALSE;
+    }
+
+    // Starting or ending with a space means that length might not be what is
+    // expected.
+    if (preg_match('/^\s|\s$/', $string)) {
+      return FALSE;
+    }
+
+    return TRUE;
+  }
+
+  /**
+   * Generates a unique random string containing letters and numbers.
+   *
+   * Do not use this method when testing unvalidated user input. Instead, use
+   * \Drupal\simpletest\TestBase::randomString().
+   *
+   * @param int $length
+   *   Length of random string to generate.
+   *
+   * @return string
+   *   Randomly generated unique string.
+   *
+   * @see \Drupal\Component\Utility\Random::name()
+   */
+  protected function randomMachineName($length = 8) {
+    return $this->getRandomGenerator()->name($length, TRUE);
+  }
+
+  /**
+   * Generates a random PHP object.
+   *
+   * @param int $size
+   *   The number of random keys to add to the object.
+   *
+   * @return \stdClass
+   *   The generated object, with the specified number of random keys. Each key
+   *   has a random string value.
+   *
+   * @see \Drupal\Component\Utility\Random::object()
+   */
+  public function randomObject($size = 4) {
+    return $this->getRandomGenerator()->object($size);
+  }
+
+  /**
+   * Gets the random generator for the utility methods.
+   *
+   * @return \Drupal\Component\Utility\Random
+   *   The random generator.
+   */
+  protected function getRandomGenerator() {
+    if (!is_object($this->randomGenerator)) {
+      $this->randomGenerator = new Random();
+    }
+    return $this->randomGenerator;
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/SessionTestTrait.php b/core/tests/Drupal/Tests/SessionTestTrait.php
new file mode 100644
index 0000000..e71fdf2
--- /dev/null
+++ b/core/tests/Drupal/Tests/SessionTestTrait.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\Tests;
+
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Provides methods to generate and get session name in tests.
+ */
+trait SessionTestTrait {
+
+  /**
+   * The name of the session cookie.
+   *
+   * @var string
+   */
+  protected $sessionName;
+
+  /**
+   * Generates a session cookie name.
+   *
+   * @param string $data
+   *   The data to generate session name.
+   */
+  protected function generateSessionName($data) {
+    $prefix = (Request::createFromGlobals()->isSecure() ? 'SSESS' : 'SESS');
+    $this->sessionName = $prefix . substr(hash('sha256', $data), 0, 32);
+  }
+
+  /**
+   * Returns the session name in use on the child site.
+   *
+   * @return string
+   *   The name of the session cookie.
+   */
+  protected function getSessionName() {
+    return $this->sessionName;
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/WebAssert.php b/core/tests/Drupal/Tests/WebAssert.php
new file mode 100644
index 0000000..d863de2
--- /dev/null
+++ b/core/tests/Drupal/Tests/WebAssert.php
@@ -0,0 +1,67 @@
+<?php
+
+namespace Drupal\Tests;
+
+use Behat\Mink\WebAssert as MinkWebAssert;
+use Behat\Mink\Element\TraversableElement;
+use Behat\Mink\Exception\ElementNotFoundException;
+
+/**
+ * Defines a class with methods for asserting presence of elements during tests.
+ */
+class WebAssert extends MinkWebAssert {
+
+  /**
+   * Checks that specific button exists on the current page.
+   *
+   * @param string $button
+   *   One of id|name|label|value for the button.
+   * @param \Behat\Mink\Element\TraversableElement $container
+   *   (optional) The document to check against. Defaults to the current page.
+   *
+   * @return \Behat\Mink\Element\NodeElement
+   *   The matching element.
+   *
+   * @throws \Behat\Mink\Exception\ElementNotFoundException
+   *   When the element doesn't exist.
+   */
+  public function buttonExists($button, TraversableElement $container = NULL) {
+    $container = $container ?: $this->session->getPage();
+    $node = $container->findButton($button);
+
+    if ($node === NULL) {
+      throw new ElementNotFoundException($this->session, 'button', 'id|name|label|value', $button);
+    }
+
+    return $node;
+  }
+
+  /**
+   * Checks that specific select field exists on the current page.
+   *
+   * @param string $select
+   *   One of id|name|label|value for the select field.
+   * @param \Behat\Mink\Element\TraversableElement $container
+   *   (optional) The document to check against. Defaults to the current page.
+   *
+   * @return \Behat\Mink\Element\NodeElement
+   *   The matching element
+   *
+   * @throws \Behat\Mink\Exception\ElementNotFoundException
+   *   When the element doesn't exist.
+   */
+  public function selectExists($select, TraversableElement $container = NULL) {
+    $container = $container ?: $this->session->getPage();
+    $node = $container->find('named', array(
+      'select',
+      $this->session->getSelectorsHandler()->xpathLiteral($select),
+    ));
+
+    if ($node === NULL) {
+      throw new ElementNotFoundException($this->session, 'select', 'id|name|label|value', $select);
+    }
+
+    return $node;
+  }
+
+}