diff --git a/core/modules/system/lib/Drupal/system/Tests/Graph/GraphUnitTest.php b/core/tests/Drupal/Tests/Component/Graph/GraphUnitTest.php
similarity index 79%
rename from core/modules/system/lib/Drupal/system/Tests/Graph/GraphUnitTest.php
rename to core/tests/Drupal/Tests/Component/Graph/GraphUnitTest.php
index a68535c..9595f03 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Graph/GraphUnitTest.php
+++ b/core/tests/Drupal/Tests/Component/Graph/GraphUnitTest.php
@@ -2,20 +2,20 @@
 
 /**
  * @file
- * Definition of Drupal\system\Tests\Graph\GraphUnitTest.
+ * Definition of Drupal\Tests\Component\Graph\GraphUnitTest.
  */
 
-namespace Drupal\system\Tests\Graph;
+namespace Drupal\Tests\Component\Graph;
 
 use Drupal\Component\Graph\Graph;
-use Drupal\simpletest\UnitTestBase;
+use Drupal\Tests\UnitTestCase;
 
 /**
  * Unit tests for the graph handling features.
  *
  * @see Drupal\Component\Graph\Graph
  */
-class GraphUnitTest extends UnitTestBase {
+class GraphUnitTest extends UnitTestCase {
   public static function getInfo() {
     return array(
       'name' => 'Directed acyclic graph manipulation',
@@ -119,7 +119,7 @@ function assertPaths($graph, $expected_paths) {
       // Build an array with keys = $paths and values = TRUE.
       $expected = array_fill_keys($paths, TRUE);
       $result = isset($graph[$vertex]['paths']) ? $graph[$vertex]['paths'] : array();
-      $this->assertEqual($expected, $result, format_string('Expected paths for vertex @vertex: @expected-paths, got @paths', array('@vertex' => $vertex, '@expected-paths' => $this->displayArray($expected, TRUE), '@paths' => $this->displayArray($result, TRUE))));
+      $this->assertEquals($expected, $result, sprintf('Expected paths for vertex %s: %s, got %s', $vertex, $this->displayArray($expected, TRUE), $this->displayArray($result, TRUE)));
     }
   }
 
@@ -137,7 +137,7 @@ function assertReversePaths($graph, $expected_reverse_paths) {
       // Build an array with keys = $paths and values = TRUE.
       $expected = array_fill_keys($paths, TRUE);
       $result = isset($graph[$vertex]['reverse_paths']) ? $graph[$vertex]['reverse_paths'] : array();
-      $this->assertEqual($expected, $result, format_string('Expected reverse paths for vertex @vertex: @expected-paths, got @paths', array('@vertex' => $vertex, '@expected-paths' => $this->displayArray($expected, TRUE), '@paths' => $this->displayArray($result, TRUE))));
+      $this->assertEquals($expected, $result, sprintf('Expected reverse paths for vertex %s: %s, got %s', $vertex, $this->displayArray($expected, TRUE), $this->displayArray($result, TRUE)));
     }
   }
 
@@ -157,9 +157,9 @@ function assertComponents($graph, $expected_components) {
         $result_components[] = $graph[$vertex]['component'];
         unset($unassigned_vertices[$vertex]);
       }
-      $this->assertEqual(1, count(array_unique($result_components)), format_string('Expected one unique component for vertices @vertices, got @components', array('@vertices' => $this->displayArray($component), '@components' => $this->displayArray($result_components))));
+      $this->assertEquals(1, count(array_unique($result_components)), sprintf('Expected one unique component for vertices %s, got %s', $this->displayArray($component), $this->displayArray($result_components)));
     }
-    $this->assertEqual(array(), $unassigned_vertices, format_string('Vertices not assigned to a component: @vertices', array('@vertices' => $this->displayArray($unassigned_vertices, TRUE))));
+    $this->assertEquals(array(), $unassigned_vertices, sprintf('Vertices not assigned to a component: %s', $this->displayArray($unassigned_vertices, TRUE)));
   }
 
   /**
@@ -174,7 +174,7 @@ function assertWeights($graph, $expected_orders) {
     foreach ($expected_orders as $order) {
       $previous_vertex = array_shift($order);
       foreach ($order as $vertex) {
-        $this->assertTrue($graph[$previous_vertex]['weight'] < $graph[$vertex]['weight'], format_string('Weights of @previous-vertex and @vertex are correct relative to each other', array('@previous-vertex' => $previous_vertex, '@vertex' => $vertex)));
+        $this->assertTrue($graph[$previous_vertex]['weight'] < $graph[$vertex]['weight'], sprintf('Weights of %s and %s are correct relative to each other', $previous_vertex, $vertex));
       }
     }
   }