diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleUpdateBase.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleUpdateBase.php
index 6554886b9c4bc0720b8187a3b5dec039a7bb658c..a7895b9c724cc93fdd41ca23c08642531d240707 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleUpdateBase.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleUpdateBase.php
@@ -12,9 +12,9 @@
 use Drupal\Component\Utility\String;
 
 /**
- * Tests for update translations.
+ * Base class for testing updates to string translations.
  */
-class LocaleUpdateBase extends WebTestBase {
+abstract class LocaleUpdateBase extends WebTestBase {
 
   /**
    * Timestamp for an old translation.
diff --git a/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuWebTestBase.php b/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuWebTestBase.php
index a8dda4b93ac51f0ca725f3409b613a8c97ce485d..5f16536e2155d41b7299830bfb08e4b6c67e1562 100644
--- a/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuWebTestBase.php
+++ b/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuWebTestBase.php
@@ -10,9 +10,9 @@
 use Drupal\simpletest\WebTestBase;
 
 /**
- * Defines a base class for menu web tests.
+ * Base class for menu web tests.
  */
-class MenuWebTestBase extends WebTestBase {
+abstract class MenuWebTestBase extends WebTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php
index 9a4b5bd14e9dd4eb2570314f826cf8f590cd2b30..39a23e2523bb19f339f3f482c85d4f66ef498f90 100644
--- a/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php
@@ -13,7 +13,10 @@
 use Drupal\migrate\Row;
 use Drupal\simpletest\WebTestBase;
 
-class MigrateTestBase extends WebTestBase implements MigrateMessageInterface {
+/**
+ * Base class for migration tests.
+ */
+abstract class MigrateTestBase extends WebTestBase implements MigrateMessageInterface {
 
   /**
    * The file path(s) to the dumped database(s) to load into the child site.
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/MigrateDrupalTestBase.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/MigrateDrupalTestBase.php
index f66010293d5f66261b92927bdfdcb5eef2831d4c..91e20ff9ea3e7c1ee2ade9ad0c5e513288d43dc0 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/MigrateDrupalTestBase.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/MigrateDrupalTestBase.php
@@ -9,7 +9,10 @@
 
 use Drupal\migrate\Tests\MigrateTestBase;
 
-class MigrateDrupalTestBase extends MigrateTestBase {
+/**
+ * Base class for Drupal migration tests.
+ */
+abstract class MigrateDrupalTestBase extends MigrateTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateNodeTestBase.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateNodeTestBase.php
index 26a4c3407ab8e5b6452c0ccc2e821e09d9720e15..e51a2d113909c1bd2a4a229aa226587a945b1500 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateNodeTestBase.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateNodeTestBase.php
@@ -9,7 +9,10 @@
 
 use Drupal\migrate_drupal\Tests\MigrateDrupalTestBase;
 
-class MigrateNodeTestBase extends MigrateDrupalTestBase {
+/**
+ * Base class for Node migration tests.
+ */
+abstract class MigrateNodeTestBase extends MigrateDrupalTestBase {
 
   static $modules = array('node');
 
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTermNodeTestBase.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTermNodeTestBase.php
index e7b64d1263a7d32c95c45daf2e89acf185af7dcb..1d8cc99620604d554ceed8cc59c094fb2b94d60a 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTermNodeTestBase.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTermNodeTestBase.php
@@ -9,7 +9,10 @@
 
 use Drupal\migrate_drupal\Tests\MigrateDrupalTestBase;
 
-class MigrateTermNodeTestBase extends MigrateDrupalTestBase {
+/**
+ * Base class for Taxonomy/Node migration tests.
+ */
+abstract class MigrateTermNodeTestBase extends MigrateDrupalTestBase {
 
   /**
    * {@inheritdoc}
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUploadBase.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUploadBase.php
index c730cf1556abf17755a51387c5db8eda7781ac24..a1d25ba5543a34df60f4916aae03a1365fa92768 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUploadBase.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUploadBase.php
@@ -9,7 +9,10 @@
 
 use Drupal\migrate_drupal\Tests\MigrateDrupalTestBase;
 
-class MigrateUploadBase extends MigrateDrupalTestBase {
+/**
+ * Base class for file/upload migration tests.
+ */
+abstract class MigrateUploadBase extends MigrateDrupalTestBase {
 
   /**
    * {@inheritdoc}
diff --git a/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesTest.php b/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesTestBase.php
similarity index 89%
rename from core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesTest.php
rename to core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesTestBase.php
index 70c527390a6706f34567818b5e82cc2a9d246827..b01e582e9b336eec08652dc3cb1f6e4f58bb7c5c 100644
--- a/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesTest.php
+++ b/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesTestBase.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Definition of Drupal\options\Tests\OptionsDynamicValuesTest.
+ * Contains \Drupal\options\Tests\OptionsDynamicValuesTestBase.
  */
 
 namespace Drupal\options\Tests;
@@ -10,9 +10,9 @@
 use Drupal\field\Tests\FieldTestBase;
 
 /**
- * Sets up a Options field for testing allowed values functions.
+ * Base class for testing allowed values of options fields.
  */
-class OptionsDynamicValuesTest extends FieldTestBase {
+abstract class OptionsDynamicValuesTestBase extends FieldTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesValidationTest.php b/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesValidationTest.php
index f978a7942c4687e866eb49eec0e8fca700f4a86c..d4648501a6684fea0d8042077f1070a9dac87c15 100644
--- a/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesValidationTest.php
+++ b/core/modules/options/lib/Drupal/options/Tests/OptionsDynamicValuesValidationTest.php
@@ -10,7 +10,7 @@
 /**
  * Tests the Options field allowed values function.
  */
-class OptionsDynamicValuesValidationTest extends OptionsDynamicValuesTest {
+class OptionsDynamicValuesValidationTest extends OptionsDynamicValuesTestBase {
   public static function getInfo() {
     return array(
       'name' => 'Options field dynamic values',
diff --git a/core/modules/options/lib/Drupal/options/Tests/OptionsFieldUnitTestBase.php b/core/modules/options/lib/Drupal/options/Tests/OptionsFieldUnitTestBase.php
index 5468547eb9da207c55a24bdb333c3d4ab07b9db4..bba78c3cd138083427e5ef541e202e0ceef5cff3 100644
--- a/core/modules/options/lib/Drupal/options/Tests/OptionsFieldUnitTestBase.php
+++ b/core/modules/options/lib/Drupal/options/Tests/OptionsFieldUnitTestBase.php
@@ -11,9 +11,9 @@
 use Drupal\field\Tests\FieldUnitTestBase;
 
 /**
- * Defines a common base test class for unit tests of the options module.
+ * Base class for Options module integration tests.
  */
-class OptionsFieldUnitTestBase extends FieldUnitTestBase {
+abstract class OptionsFieldUnitTestBase extends FieldUnitTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/options/lib/Drupal/options/Tests/OptionsSelectDynamicValuesTest.php b/core/modules/options/lib/Drupal/options/Tests/OptionsSelectDynamicValuesTest.php
index 5ddcf0f4efa20bed11f5b2ea0d3ef540f15ecb7f..3fee9c5e8bac040d1fa55b3808df6788721041ba 100644
--- a/core/modules/options/lib/Drupal/options/Tests/OptionsSelectDynamicValuesTest.php
+++ b/core/modules/options/lib/Drupal/options/Tests/OptionsSelectDynamicValuesTest.php
@@ -10,7 +10,7 @@
 /**
  * Tests an options select with a dynamic allowed values function.
  */
-class OptionsSelectDynamicValuesTest extends OptionsDynamicValuesTest {
+class OptionsSelectDynamicValuesTest extends OptionsDynamicValuesTestBase {
   public static function getInfo() {
     return array(
       'name' => 'Options select dynamic values',
diff --git a/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditTestBase.php b/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditTestBase.php
index 4fc19edd8e057fa127bb5d03751a16ee7bdc0e6b..c72899bc838a1669dc83565a45be0d94f4311669 100644
--- a/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditTestBase.php
+++ b/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditTestBase.php
@@ -10,9 +10,9 @@
 use Drupal\simpletest\DrupalUnitTestBase;
 
 /**
- * Parent class for Quick Edit tests.
+ * Base class for testing Quick Edit functionality.
  */
-class QuickEditTestBase extends DrupalUnitTestBase {
+abstract class QuickEditTestBase extends DrupalUnitTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/system/lib/Drupal/system/Tests/Module/ModuleEnableTest.php b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleEnableTest.php
deleted file mode 100644
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..0000000000000000000000000000000000000000
diff --git a/core/modules/system/lib/Drupal/system/Tests/Path/PathUnitTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Path/PathUnitTestBase.php
index 64a92ea6ff2fd14ccd552fd6c5cc6ff243ecdad7..4807d47ab952fc44b8049d13ef0ccc443e3230ee 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Path/PathUnitTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Path/PathUnitTestBase.php
@@ -11,9 +11,9 @@
 use Drupal\Core\Database\Database;
 
 /**
- * Defines a base class for path unit testing.
+ * Base class for Path/URL alias integration tests.
  */
-class PathUnitTestBase extends DrupalUnitTestBase {
+abstract class PathUnitTestBase extends DrupalUnitTestBase {
 
   public function setUp() {
     parent::setUp();
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/DiscoveryTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/DiscoveryTestBase.php
index 20a574a6fde8f5f31cba28701fb130f97489fdde..aa5cf5b1e8105ac42c661b8da51098153afb11d7 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/DiscoveryTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/DiscoveryTestBase.php
@@ -10,9 +10,9 @@
 use Drupal\simpletest\UnitTestBase;
 
 /**
- * Tests that plugins are correctly discovered.
+ * Base class for plugin discovery tests.
  */
-class DiscoveryTestBase extends UnitTestBase {
+abstract class DiscoveryTestBase extends UnitTestBase {
 
   /**
    * The discovery component to test.
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php b/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php
index 630cb8382ea5552f9772ef94a72a20a1c6ccaf90..c13bd4c33e1db8d0eec2f300175a654eeda13afc 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php
@@ -11,9 +11,9 @@
 use Drupal\system\Tests\Entity\EntityUnitTestBase;
 
 /**
- * Test token replacement in strings.
+ * Base class for token replacement tests.
  */
-class TokenReplaceUnitTestBase extends EntityUnitTestBase {
+abstract class TokenReplaceUnitTestBase extends EntityUnitTestBase {
 
   /**
    * The interface language.
diff --git a/core/modules/tour/lib/Drupal/tour/Tests/TourTestBase.php b/core/modules/tour/lib/Drupal/tour/Tests/TourTestBase.php
index 0beb7f0737327ee52f3114d472d5b8fd85498c06..c6372cde9a1b1ed8d260da39586bea423dac3050 100644
--- a/core/modules/tour/lib/Drupal/tour/Tests/TourTestBase.php
+++ b/core/modules/tour/lib/Drupal/tour/Tests/TourTestBase.php
@@ -10,9 +10,9 @@
 use Drupal\simpletest\WebTestBase;
 
 /**
- * Tests tour functionality.
+ * Base class for testing Tour functionality.
  */
-class TourTestBase extends WebTestBase {
+abstract class TourTestBase extends WebTestBase {
 
   /**
    * Assert function to determine if tips rendered to the page