diff --git a/core/phpunit.xml.dist b/core/phpunit.xml.dist
index 6ca7e89..60f359d 100644
--- a/core/phpunit.xml.dist
+++ b/core/phpunit.xml.dist
@@ -3,14 +3,15 @@
 <phpunit bootstrap="tests/bootstrap.php" colors="true">
   <testsuites>
     <testsuite name="Drupal Unit Test Suite">
-      <directory>./tests/*</directory>
-      <directory>./modules/*/tests/*</directory>
-      <directory>../modules/*/tests/*</directory>
-      <directory>../sites/*/modules/*/tests/*</directory>
+      <directory>./tests/</directory>
+      <directory>./modules/*/tests/</directory>
       <!-- Exclude files that end in Test.php that aren't actually phpunit tests. -->
       <exclude>./modules/config/tests/config_test/lib/Drupal/config_test</exclude>
       <exclude>./modules/views/tests/views_test_data/lib/Drupal/views_test_data</exclude>
     </testsuite>
+    <testsuite name="Drupal Contributed Module Unit Test Suite">
+      <directory>../modules/</directory>
+      <directory>../sites/</directory>
+    </testsuite>
   </testsuites>
 </phpunit>
-
diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index 08d8871..ec1bfa4 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -1,20 +1,55 @@
 <?php
 
-// Register the namespaces we'll need to autoload from.
+/**
+ * @file
+ * Autoloader for Drupal PHPUnit testing.
+ *
+ * @see phpunit.xml.dist
+ */
+
+/**
+ * Recursively scan a directory for modules to autoload.
+ *
+ * For our purposes here, a module is considered to be
+ * a directory with a /lib subdirectory.
+ */
+function _drupal_phpunit_scan_autoload_directories($loader, $given_path) {
+  // Make sure we ignore . and .. directories.
+  if (in_array(basename($given_path), array('.', '..'))) {
+    return;
+  }
+  $items = scandir($given_path);
+  foreach($items as $item) {
+    $child_path = "$given_path/$item";
+    // We only care about directories.
+    if (is_dir($child_path)) {
+      // Recursion first.
+      _drupal_phpunit_scan_autoload_directories($loader, $child_path);
+      // Check if it's a module second.
+      $lib_path = $child_path . '/lib';
+      if (is_dir($lib_path)) {
+        $loader->add('Drupal\\' . $item, $lib_path);
+      }
+    }
+  }
+}
+
+// Start with classes in known locations.
 $loader = require __DIR__ . "/../vendor/autoload.php";
 $loader->add('Drupal\\', __DIR__);
 $loader->add('Drupal\Core', __DIR__ . "/../../core/lib");
 $loader->add('Drupal\Component', __DIR__ . "/../../core/lib");
 
-foreach (scandir(__DIR__ . "/../modules") as $module) {
-  $loader->add('Drupal\\' . $module, __DIR__ . "/../modules/" . $module . "/lib");
-  // Add test module classes.
-  $test_modules_dir = __DIR__ . "/../modules/$module/tests/modules";
-  if (is_dir($test_modules_dir)) {
-    foreach (scandir($test_modules_dir) as $test_module) {
-      $loader->add('Drupal\\' . $test_module, $test_modules_dir . '/' . $test_module . '/lib');
-    }
-  }
+// Scan these directories for modules to autoload.
+$autoload_these_paths = array(
+  __DIR__ . "/../modules",
+  __DIR__ . "/../../modules",
+  __DIR__ . "/../../sites",
+);
+
+// Scan through the directories.
+foreach($autoload_these_paths as $path) {
+  _drupal_phpunit_scan_autoload_directories($loader, $path);
 }
 
 require __DIR__ . "/../../core/lib/Drupal.php";