diff --git a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
index 68485b6..f1586cc 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
@@ -29,6 +29,20 @@
 abstract class DrupalUnitTestBase extends UnitTestBase {
 
   /**
+   * Modules to enable.
+   *
+   * Test classes extending this class, and any classes in the hierarchy up to
+   * this class, may specify individual lists of modules to enable by setting
+   * this property. The values of all properties in all classes in the hierarchy
+   * are merged.
+   *
+   * @see DrupalUnitTestBase::setUp()
+   *
+   * @var array
+   */
+  public static $modules = array();
+
+  /**
    * Fixed module list being used by this test.
    *
    * @var array