diff --git a/core/tests/Drupal/Tests/Component/Plugin/DefaultFactoryTest.php b/core/tests/Drupal/Tests/Component/Plugin/DefaultFactoryTest.php
index 0d12fac..ed53798 100644
--- a/core/tests/Drupal/Tests/Component/Plugin/DefaultFactoryTest.php
+++ b/core/tests/Drupal/Tests/Component/Plugin/DefaultFactoryTest.php
@@ -7,7 +7,74 @@
 
 namespace Drupal\Tests\Component\Plugin;
 
-class DefaultFactoryTest {
+use Drupal\Component\Plugin\Factory\DefaultFactory;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Component\Plugin\DefaultFactory
+ */
+class DefaultFactoryTest extends UnitTestCase {
+
+  /**
+   * Tests getPluginClass() with a valid plugin.
+   *
+   * @covers ::getPluginClass
+   */
+  public function testGetPluginClassWithValidPlugin() {
+    $plugin_class = 'Drupal\plugin_test\Plugin\plugin_test\fruit\Cherry';
+    $class = DefaultFactory::getPluginClass('cherry', ['class' => $plugin_class]);
+
+    $this->assertEquals($plugin_class, $class);
+  }
+
+  /**
+   * Tests getPluginClass() with a missing class definition.
+   *
+   * @covers ::getPluginClass
+   *
+   * @expectedException \Drupal\Component\Plugin\Exception\PluginException
+   * @expectedExceptionMessage The plugin (cherry) did not specify an instance class.
+   */
+  public function testGetPluginClassWithMissingClass() {
+    DefaultFactory::getPluginClass('cherry', []);
+  }
+
+  /**
+   * Tests getPluginClass() with a not existing class definition.
+   *
+   * @covers ::getPluginClass
+   *
+   * @expectedException \Drupal\Component\Plugin\Exception\PluginException
+   * @expectedExceptionMessage Plugin (kiwifruit) instance class "\Drupal\plugin_test\Plugin\plugin_test\fruit\Kiwifruit" does not exist.
+   */
+  public function testGetPluginClassWithNotExistingClass() {
+    DefaultFactory::getPluginClass('kiwifruit', ['class' => '\Drupal\plugin_test\Plugin\plugin_test\fruit\Kiwifruit']);
+  }
+
+  /**
+   * Tests getPluginClass() with a required interface.
+   *
+   * @covers ::getPluginClass
+   */
+  public function testGetPluginClassWithInterface() {
+    $plugin_class = 'Drupal\plugin_test\Plugin\plugin_test\fruit\Cherry';
+    $class = DefaultFactory::getPluginClass('cherry', ['class' => $plugin_class], '\Drupal\plugin_test\Plugin\plugin_test\fruit\FruitInterface');
+
+    $this->assertEquals($plugin_class, $class);
+  }
+
+  /**
+   * Tests getPluginClass() with a required interface but no implementation.
+   *
+   * @covers ::getPluginClass
+   *
+   * @expectedException \Drupal\Component\Plugin\Exception\PluginException
+   * @expectedExceptionMessage Plugin "cherry" (Drupal\plugin_test\Plugin\plugin_test\fruit\Kale) in core should implement interface \Drupal\plugin_test\Plugin\plugin_test\fruit\FruitInterface.
+   */
+  public function testGetPluginClassWithInterfaceAndInvalidClass() {
+    $plugin_class = 'Drupal\plugin_test\Plugin\plugin_test\fruit\Kale';
+    DefaultFactory::getPluginClass('cherry', ['class' => $plugin_class, 'provider' => 'core'], '\Drupal\plugin_test\Plugin\plugin_test\fruit\FruitInterface');
+  }
 
 }
 
diff --git a/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php b/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php
index 407a916..c1c2d7f 100644
--- a/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php
+++ b/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php
@@ -38,7 +38,7 @@ public function __construct(\Traversable $namespaces, array $definitions, Module
     // discovery implementation, but StaticDiscovery lets us add some simple
     // mock plugins for unit testing.
     $this->discovery = new StaticDiscovery();
-    $this->factory = new DefaultFactory($this->discovery);
+    $this->factory = new DefaultFactory($this->discovery, $interface);
 
     // Add the static definitions.
     foreach ($definitions as $key => $definition) {
@@ -50,7 +50,6 @@ public function __construct(\Traversable $namespaces, array $definitions, Module
     if ($alter_hook) {
       $this->alterInfo($alter_hook);
     }
-    $this->interface = $interface;
   }
 
 }