diff --git a/src/unit/engine/PhutilUnitTestEngine.php b/src/unit/engine/PhutilUnitTestEngine.php
--- a/src/unit/engine/PhutilUnitTestEngine.php
+++ b/src/unit/engine/PhutilUnitTestEngine.php
@@ -205,12 +205,18 @@
         continue;
       }
 
-      do {
+      while ($library_path) {
+        if ($library_path == '.') {
+          $library_path = '';
+        }
+
         $paths[$library_name.':'.$library_path] = array(
           'library' => $library_name,
-          'path'    => $library_path.'/__tests__/',
+          'path'    => ($library_path ? $library_path.'/' : '').'__tests__/',
         );
-      } while (($library_path = dirname($library_path)) != '.');
+
+        $library_path = dirname($library_path);
+      }
     }
 
     return $paths;
diff --git a/src/unit/engine/__tests__/PhutilUnitTestEngineTestCase.php b/src/unit/engine/__tests__/PhutilUnitTestEngineTestCase.php
--- a/src/unit/engine/__tests__/PhutilUnitTestEngineTestCase.php
+++ b/src/unit/engine/__tests__/PhutilUnitTestEngineTestCase.php
@@ -142,6 +142,7 @@
 
           dirname(dirname(__FILE__)).'/__tests__/',
           dirname(dirname(dirname(__FILE__))).'/__tests__/',
+          phutil_get_library_root('arcanist').'/__tests__/',
         ),
       ),
       'normal directory' => array(
@@ -151,11 +152,12 @@
         array(
           dirname(dirname(__FILE__)).'/__tests__/',
           dirname(dirname(dirname(__FILE__))).'/__tests__/',
+          phutil_get_library_root('arcanist').'/__tests__/',
         ),
       ),
       'library root' => array(
-        array(phutil_get_library_root()),
-        array(phutil_get_library_root().'/__tests__/'),
+        array(phutil_get_library_root('arcanist')),
+        array(phutil_get_library_root('arcanist').'/__tests__/'),
       ),
     );
 
@@ -163,10 +165,10 @@
       ->setWorkingCopy($this->getWorkingCopy());
 
     foreach ($tests as $name => $test) {
-      list($paths, $tests) = $test;
+      list($paths, $test_paths) = $test;
       $expected = array();
 
-      foreach ($tests as $path) {
+      foreach ($test_paths as $path) {
         $library_root = phutil_get_library_root_for_path($path);
         $library = phutil_get_library_name_for_root($library_root);