reverted:
--- b/core/tests/Drupal/Tests/UnitTestCase.php
+++ a/core/tests/Drupal/Tests/UnitTestCase.php
@@ -42,11 +42,6 @@
     \Drupal::unsetContainer();
 
     $this->root = dirname(dirname(substr(__DIR__, 0, -strlen(__NAMESPACE__))));
-
-    // Ensure that tests are in the Drupal\Tests namespace.
-    if (__NAMESPACE__ != 'Drupal\Tests' && strpos(__NAMESPACE__, 'Drupal\Tests\\', 0) !== 0) {
-      throw new \Exception('Unit tests must be in the "Drupal\Tests" namespace.');
-    }
   }
 
   /**
reverted:
--- b/core/tests/Drupal/UnitTestCaseTest/UnitTestCaseTest.php
+++ /dev/null
@@ -1,40 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\UnitTestCaseTest\UnitTestCaseTest.
- */
-
-// Note: this test is in an "invalid" namespace on purpose.
-// All tests ought to be in "Drupal\Tests".
-namespace Drupal\UnitTestCaseTest;
-
-use Drupal\Tests\UnitTestCase;
-
-/**
- * Provides a test for the namespace enforcement in UnitTestCase::setUp().
- *
- * @coversDefaultClass \Drupal\Tests\UnitTestCase
- * @group simpletest
- */
-class UnitTestCaseTest extends UnitTestCase {
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    // Do nothing, as running parent::setUp() will throw an exception.
-  }
-
-  /**
-   * @covers ::setUp
-   *
-   * @expectedException        Exception
-   * @expectedExceptionMessage Unit tests must be in the "Drupal\Tests" namespace.
-   */
-  public function testSetUp() {
-    // This should throw the exception listed in the annotation.
-    parent::setUp();
-  }
-
-}
diff -u b/core/tests/bootstrap.php b/core/tests/bootstrap.php
--- b/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -70,7 +70,7 @@
 // Start with classes in known locations.
 $loader = require __DIR__ . '/../../autoload.php';
 $loader->add('Drupal\\Tests', __DIR__);
-$loader->add('Drupal\\UnitTestCaseTest', __DIR__);
+$loader->add('Drupal\\DrupalStandardsListenerTest', __DIR__);
 
 // Scan for arbitrary extension namespaces from core and contrib.
 $extension_roots = array_merge(array(
only in patch2:
unchanged:
--- a/core/tests/Drupal/Tests/Standards/DrupalStandardsListener.php
+++ b/core/tests/Drupal/Tests/Standards/DrupalStandardsListener.php
@@ -16,6 +16,13 @@
 class DrupalStandardsListener extends \PHPUnit_Framework_BaseTestListener {
 
   /**
+   * Saves the classes that fail the namespace check.
+   *
+   * @var array
+   */
+  protected $namespaceCheckFailedClasses = array();
+
+  /**
    * Signals a coding standards failure to the user.
    *
    * @param \PHPUnit_Framework_TestCase $test
@@ -144,6 +151,24 @@ public function checkValidCoversForTest(\PHPUnit_Framework_TestCase $test) {
   }
 
   /**
+   * Checks that tests are in the Drupal\Tests namespace. 
+   *
+   * @param \PHPUnit_Framework_Test $test
+   *   The test where we should insert our test failure.
+   */
+  protected function checkValidNamespaceForTest(\PHPUnit_Framework_Test $test) {
+    $class = get_class($test);
+    if (!in_array($class, $this->namespaceCheckFailedClasses) && strpos($class, 'Drupal\Tests\\', 0) !== 0) {
+      // For the unit test of this method we run endTest() twice, but we don't
+      // want to run this namespace check a second time as the test failure
+      // would go uncaught.
+      $this->namespaceCheckFailedClasses[] = $class;
+      $test->assertTrue(FALSE, 'Test is not in the Drupal\Tests namespace.');
+    }
+  }
+
+
+  /**
    * {@inheritdoc}
    */
   public function endTest(\PHPUnit_Framework_Test $test, $time) {
@@ -152,6 +177,7 @@ public function endTest(\PHPUnit_Framework_Test $test, $time) {
     // subclasses.
     if ($test instanceof \PHPUnit_Framework_TestCase) {
       $this->checkValidCoversForTest($test);
+      $this->checkValidNamespaceForTest($test);
     }
     elseif ($test instanceof \PHPUnit_Framework_TestSuite) {
       foreach ($test->getGroupDetails() as $tests) {