diff -u b/core/modules/migrate_drupal/tests/fixtures/drupal7.php b/core/modules/migrate_drupal/tests/fixtures/drupal7.php
--- b/core/modules/migrate_drupal/tests/fixtures/drupal7.php
+++ b/core/modules/migrate_drupal/tests/fixtures/drupal7.php
@@ -41532,12 +41532,16 @@
   'value' => 'i:1024;',
 ))
 ->values(array(
+  'name' => 'theme_bartik_settings',
+  'value' => 'a:18:{s:11:"toggle_logo";i:1;s:11:"toggle_name";i:1;s:13:"toggle_slogan";i:1;s:24:"toggle_node_user_picture";i:1;s:27:"toggle_comment_user_picture";i:1;s:32:"toggle_comment_user_verification";i:1;s:14:"toggle_favicon";i:1;s:16:"toggle_main_menu";i:1;s:21:"toggle_secondary_menu";i:1;s:12:"default_logo";i:0;s:9:"logo_path";s:16:"public://gnu.png";s:15:"default_favicon";i:1;s:12:"favicon_path";s:0:"";s:14:"favicon_upload";s:0:"";s:6:"scheme";s:7:"default";s:7:"palette";a:9:{s:3:"top";s:7:"#0779bf";s:6:"bottom";s:7:"#48a9e4";s:2:"bg";s:7:"#ffffff";s:7:"sidebar";s:7:"#f6f6f2";s:14:"sidebarborders";s:7:"#f9f9f9";s:6:"footer";s:7:"#292929";s:11:"titleslogan";s:7:"#fffeff";s:4:"text";s:7:"#3b3b3b";s:4:"link";s:7:"#0071B3";}s:5:"theme";s:6:"bartik";s:4:"info";a:12:{s:6:"fields";a:9:{s:3:"top";s:10:"Header top";s:6:"bottom";s:13:"Header bottom";s:2:"bg";s:15:"Main background";s:7:"sidebar";s:18:"Sidebar background";s:14:"sidebarborders";s:15:"Sidebar borders";s:6:"footer";s:17:"Footer background";s:11:"titleslogan";s:16:"Title and slogan";s:4:"text";s:10:"Text color";s:4:"link";s:10:"Link color";}s:7:"schemes";a:6:{s:7:"default";a:2:{s:5:"title";s:21:"Blue Lagoon (default)";s:6:"colors";a:9:{s:3:"top";s:7:"#0779bf";s:6:"bottom";s:7:"#48a9e4";s:2:"bg";s:7:"#ffffff";s:7:"sidebar";s:7:"#f6f6f2";s:14:"sidebarborders";s:7:"#f9f9f9";s:6:"footer";s:7:"#292929";s:11:"titleslogan";s:7:"#fffeff";s:4:"text";s:7:"#3b3b3b";s:4:"link";s:7:"#0071B3";}}s:9:"firehouse";a:2:{s:5:"title";s:9:"Firehouse";s:6:"colors";a:9:{s:3:"top";s:7:"#cd2d2d";s:6:"bottom";s:7:"#cf3535";s:2:"bg";s:7:"#ffffff";s:7:"sidebar";s:7:"#f1f4f0";s:14:"sidebarborders";s:7:"#ededed";s:6:"footer";s:7:"#1f1d1c";s:11:"titleslogan";s:7:"#fffeff";s:4:"text";s:7:"#3b3b3b";s:4:"link";s:7:"#d6121f";}}s:3:"ice";a:2:{s:5:"title";s:3:"Ice";s:6:"colors";a:9:{s:3:"top";s:7:"#d0d0d0";s:6:"bottom";s:7:"#c2c4c5";s:2:"bg";s:7:"#ffffff";s:7:"sidebar";s:7:"#ffffff";s:14:"sidebarborders";s:7:"#cccccc";s:6:"footer";s:7:"#24272c";s:11:"titleslogan";s:7:"#000000";s:4:"text";s:7:"#4a4a4a";s:4:"link";s:7:"#019dbf";}}s:4:"plum";a:2:{s:5:"title";s:4:"Plum";s:6:"colors";a:9:{s:3:"top";s:7:"#4c1c58";s:6:"bottom";s:7:"#593662";s:2:"bg";s:7:"#fffdf7";s:7:"sidebar";s:7:"#edede7";s:14:"sidebarborders";s:7:"#e7e7e7";s:6:"footer";s:7:"#2c2c28";s:11:"titleslogan";s:7:"#ffffff";s:4:"text";s:7:"#301313";s:4:"link";s:7:"#9d408d";}}s:5:"slate";a:2:{s:5:"title";s:5:"Slate";s:6:"colors";a:9:{s:3:"top";s:7:"#4a4a4a";s:6:"bottom";s:7:"#4e4e4e";s:2:"bg";s:7:"#ffffff";s:7:"sidebar";s:7:"#ffffff";s:14:"sidebarborders";s:7:"#d0d0d0";s:6:"footer";s:7:"#161617";s:11:"titleslogan";s:7:"#ffffff";s:4:"text";s:7:"#3b3b3b";s:4:"link";s:7:"#0073b6";}}s:0:"";a:2:{s:5:"title";s:6:"Custom";s:6:"colors";a:0:{}}}s:3:"css";a:1:{i:0;s:14:"css/colors.css";}s:4:"copy";a:1:{i:0;s:8:"logo.png";}s:9:"gradients";a:1:{i:0;a:3:{s:9:"dimension";a:4:{i:0;i:0;i:1;i:0;i:2;i:0;i:3;i:0;}s:9:"direction";s:8:"vertical";s:6:"colors";a:2:{i:0;s:3:"top";i:1;s:6:"bottom";}}}s:4:"fill";a:0:{}s:6:"slices";a:0:{}s:12:"blend_target";s:7:"#ffffff";s:11:"preview_css";s:17:"color/preview.css";s:10:"preview_js";s:16:"color/preview.js";s:12:"preview_html";s:18:"color/preview.html";s:10:"base_image";s:14:"color/base.png";}}',
+))
+->values(array(
   'name' => 'theme_default',
   'value' => 's:6:"bartik";',
 ))
 ->values(array(
   'name' => 'theme_seven_settings',
-  'value' => 'a:15:{s:11:"toggle_logo";i:1;s:11:"toggle_name";i:1;s:13:"toggle_slogan";i:1;s:24:"toggle_node_user_picture";i:1;s:27:"toggle_comment_user_picture";i:0;s:32:"toggle_comment_user_verification";i:1;s:14:"toggle_favicon";i:1;s:16:"toggle_main_menu";i:1;s:21:"toggle_secondary_menu";i:0;s:12:"default_logo";i:1;s:9:"logo_path";s:0:"";s:11:"logo_upload";s:0:"";s:15:"default_favicon";i:1;s:12:"favicon_path";s:0:"";s:14:"favicon_upload";s:0:"";}',    
+  'value' => 'a:15:{s:11:"toggle_logo";i:1;s:11:"toggle_name";i:1;s:13:"toggle_slogan";i:1;s:24:"toggle_node_user_picture";i:1;s:27:"toggle_comment_user_picture";i:0;s:32:"toggle_comment_user_verification";i:1;s:14:"toggle_favicon";i:1;s:16:"toggle_main_menu";i:1;s:21:"toggle_secondary_menu";i:0;s:12:"default_logo";i:1;s:9:"logo_path";s:0:"";s:11:"logo_upload";s:0:"";s:15:"default_favicon";i:1;s:12:"favicon_path";s:0:"";s:14:"favicon_upload";s:0:"";}',
 ))
 ->values(array(
   'name' => 'tracker_batch_size',
reverted:
--- b/core/modules/system/src/Plugin/migrate/process/d7/Explode.php
+++ /dev/null
@@ -1,42 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\system\Plugin\migrate\process\d7\Explode.
- */
-
-namespace Drupal\system\Plugin\migrate\process\d7;
-
-use Drupal\Component\Utility\NestedArray;
-use Drupal\migrate\ProcessPluginBase;
-use Drupal\migrate\MigrateException;
-use Drupal\migrate\MigrateExecutableInterface;
-use Drupal\migrate\Row;
-
-/**
- * This plugin explodes a value.
- *
- * @MigrateProcessPlugin(
- *   id = "explode"
- * )
- */
-class Explode extends ProcessPluginBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    if (is_string($value[0])) {
-      if (!empty($this->configuration['delimiter'])) {
-        return explode($this->configuration['delimiter'], $value[0]);
-      }
-      else {
-        throw new MigrateException(sprintf('delimiter is empty', var_export($value, TRUE)));
-      }
-    }
-    else {
-      throw new MigrateException(sprintf('%s is not a string', var_export($value, TRUE)));
-    }
-  }
-
-}
diff -u b/core/modules/system/src/Tests/Migrate/d7/MigrateThemeSettingsTest.php b/core/modules/system/src/Tests/Migrate/d7/MigrateThemeSettingsTest.php
--- b/core/modules/system/src/Tests/Migrate/d7/MigrateThemeSettingsTest.php
+++ b/core/modules/system/src/Tests/Migrate/d7/MigrateThemeSettingsTest.php
@@ -26,6 +26,17 @@
    */
   protected function setUp() {
     parent::setUp();
+
+    // Set Bartik and Seven as the default public and admin theme.
+    $config = $this->config('system.theme');
+    $config->set('default', 'bartik');
+    $config->set('admin', 'seven');
+    $config->save();
+
+    // Install one of D8's test themes.
+    \Drupal::service('theme_handler')->install(['bartik']);
+    // Install one of D8's test themes.
+    \Drupal::service('theme_handler')->install(['seven']);
     $this->executeMigration('d7_theme_settings');
   }
 
@@ -33,8 +44,36 @@
    * Tests migration of system's variables to configuration.
    */
   public function testMigrateThemeSettings() {
+    $config = $this->config('bartik.settings');
+    $this->assertIdentical('', $config->get('favicon.path'));
+    $this->assertTrue($config->get('favicon.use_default'));
+
+    $this->assertTrue($config->get('features.comment_user_picture'));
+    $this->assertTrue($config->get('features.comment_user_verification'));
+    $this->assertTrue($config->get('features.favicon'));
+    $this->assertTrue($config->get('features.node_user_picture'));
+    $this->assertFalse($config->get('features.logo'));
+    $this->assertTrue($config->get('features.name'));
+    $this->assertTrue($config->get('features.slogan'));
+
+    $this->assertIdentical('public://gnu.png', $config->get('logo.path'));
+    $this->assertFalse($config->get('logo.use_default'));
+
+
     $config = $this->config('seven.settings');
-    // @TODO: need assertions!
+    $this->assertIdentical('', $config->get('favicon.path'));
+    $this->assertTrue($config->get('favicon.use_default'));
+
+    $this->assertFalse($config->get('features.comment_user_picture'));
+    $this->assertTrue($config->get('features.comment_user_verification'));
+    $this->assertTrue($config->get('features.favicon'));
+    $this->assertTrue($config->get('features.node_user_picture'));
+    $this->assertFalse($config->get('features.logo'));
+    $this->assertTrue($config->get('features.name'));
+    $this->assertTrue($config->get('features.slogan'));
+
+    $this->assertIdentical('', $config->get('logo.path'));
+    $this->assertTrue($config->get('logo.use_default'));
   }
 
 }
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/process/Explode.php
@@ -0,0 +1,41 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\migrate_drupal\Plugin\migrate\process\Explode.
+ */
+
+namespace Drupal\migrate_drupal\Plugin\migrate\process;
+
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\MigrateException;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Row;
+
+/**
+ * This plugin explodes a value.
+ *
+ * @MigrateProcessPlugin(
+ *   id = "explode"
+ * )
+ */
+class Explode extends ProcessPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    if (is_string($value[0])) {
+      if (!empty($this->configuration['delimiter'])) {
+        return explode($this->configuration['delimiter'], $value[0]);
+      }
+      else {
+        throw new MigrateException(sprintf('delimiter is empty', var_export($value, TRUE)));
+      }
+    }
+    else {
+      throw new MigrateException(sprintf('%s is not a string', var_export($value, TRUE)));
+    }
+  }
+
+}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/migrate_drupal/tests/src/Unit/process/ExplodeTest.php
@@ -0,0 +1,82 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\migrate_drupal\Unit\Plugin\migrate\process\ExplodeTest.
+ */
+
+namespace Drupal\Tests\migrate_drupal\Unit\Plugin\migrate\process;
+
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\migrate\Plugin\MigrateProcessInterface;
+use Drupal\migrate_drupal\Plugin\migrate\process\Explode;
+use Drupal\Tests\migrate\Unit\process\MigrateProcessTestCase;
+
+/**
+ * Tests the Explode process plugin.
+ *
+ * @group migrate_drupal
+ */
+class ExplodeTest extends MigrateProcessTestCase {
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * The migration plugin.
+   *
+   * @var \Drupal\migrate\Plugin\MigrateProcessInterface
+   */
+  protected $migrationPlugin;
+
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    $this->moduleHandler = $this->prophesize(ModuleHandlerInterface::class);
+    $this->migrationPlugin = $this->prophesize(MigrateProcessInterface::class);
+    parent::setUp();
+  }
+
+  /**
+   * Tests the transform process.
+   */
+  public function testTransform() {
+    $configuration['delimiter'] = '_';
+    $this->plugin = new Explode($configuration, 'explode', [], $this->moduleHandler->reveal(), $this->migrationPlugin->reveal());
+    $source = ['color_bartik_stylesheets'];
+    $result = ['color', 'bartik', 'stylesheets'];
+    $transformed_value = $this->plugin->transform($source, $this->migrateExecutable, $this->row, 'destinationproperty');
+    $this->assertSame($result, $transformed_value);
+  }
+
+  /**
+   * Tests invalid input.
+   *
+   * @expectedException \Drupal\migrate\MigrateException
+   * @expectedExceptionMessage is not a string
+   */
+  public function testSourceString() {
+    $configuration['delimiter'] = '_';
+    $this->plugin = new Explode($configuration, 'explode', [], $this->moduleHandler->reveal(), $this->migrationPlugin->reveal());
+    $this->plugin->transform([ ['color_bartik_stylesheets'] ], $this->migrateExecutable, $this->row, 'destinationproperty');
+  }
+
+  /**
+   * Tests empty delimter.
+   *
+   * @expectedException \Drupal\migrate\MigrateException
+   * @expectedExceptionMessage delimiter is empty
+   */
+  public function testDelimiterEmpty() {
+    $configuration['delimiter'] = '';
+    $this->plugin = new Explode($configuration, 'explode', [], $this->moduleHandler->reveal(), $this->migrationPlugin->reveal());
+    $this->plugin->transform(['color_bartik_stylesheets'], $this->migrateExecutable, $this->row, 'destinationproperty');
+  }
+
+}