diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index 92f9b85..e2546d2 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -35,7 +35,7 @@
  *
  * @ingroup testing
  */
-abstract class KernelTestBase extends UnitTestBase {
+abstract class KernelTestBase extends TestBase {
 
   use AssertContentTrait;
 
@@ -47,8 +47,8 @@
    * this property. The values of all properties in all classes in the hierarchy
    * are merged.
    *
-   * Unlike UnitTestBase::setUp(), any modules specified in the $modules
-   * property are automatically loaded and set as the fixed module list.
+   * Any modules specified in the $modules property are automatically loaded and
+   * set as the fixed module list.
    *
    * Unlike WebTestBase::setUp(), the specified modules are loaded only, but not
    * automatically installed. Modules need to be installed manually, if needed.
@@ -212,9 +212,9 @@ protected function setUp() {
     // StreamWrapper APIs.
     // @todo Move StreamWrapper management into DrupalKernel.
     // @see https://drupal.org/node/2028109
+    file_prepare_directory($this->public_files_directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
+    $this->settingsSet('file_public_path', $this->public_files_directory);
     $this->streamWrappers = array();
-    // The public stream wrapper only depends on the file_public_path setting,
-    // which is provided by UnitTestBase::setUp().
     $this->registerStreamWrapper('public', 'Drupal\Core\StreamWrapper\PublicStream');
     // The temporary stream wrapper is able to operate both with and without
     // configuration.
diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index 9819e33..2ec8a6d 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -1058,7 +1058,6 @@ private function prepareEnvironment() {
 
     // Unregister all custom stream wrappers of the parent site.
     // Availability of Drupal stream wrappers varies by test base class:
-    // - UnitTestBase operates in a completely empty environment.
     // - KernelTestBase supports and maintains stream wrappers in a custom
     //   way.
     // - WebTestBase re-initializes Drupal stream wrappers after installation.
diff --git a/core/modules/simpletest/src/UnitTestBase.php b/core/modules/simpletest/src/UnitTestBase.php
deleted file mode 100644
index 9d93fa0..0000000
--- a/core/modules/simpletest/src/UnitTestBase.php
+++ /dev/null
@@ -1,43 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\simpletest\UnitTestBase.
- */
-
-namespace Drupal\simpletest;
-
-use Drupal\Core\Database\Database;
-use Drupal\Core\Database\ConnectionNotDefinedException;
-
-/**
- * Base test case class for unit tests.
- *
- * These tests can not access the database nor files. Calling any Drupal
- * function that needs the database will throw exceptions. These include
- * watchdog(), \Drupal::moduleHandler()->getImplementations(),
- * \Drupal::moduleHandler()->invokeAll() etc.
- */
-abstract class UnitTestBase extends TestBase {
-
-  /**
-   * Constructor for UnitTestBase.
-   */
-  function __construct($test_id = NULL) {
-    parent::__construct($test_id);
-    $this->skipClasses[__CLASS__] = TRUE;
-  }
-
-  /**
-   * Sets up unit test environment.
-   *
-   * Unlike \Drupal\simpletest\WebTestBase::setUp(), UnitTestBase::setUp() does
-   * not install modules because tests are performed without accessing the
-   * database. Any required files must be explicitly included by the child class
-   * setUp() method.
-   */
-  protected function setUp() {
-    file_prepare_directory($this->public_files_directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
-    $this->settingsSet('file_public_path', $this->public_files_directory);
-  }
-}