diff --git a/src/unit/engine/PhpunitTestEngine.php b/src/unit/engine/PhpunitTestEngine.php
--- a/src/unit/engine/PhpunitTestEngine.php
+++ b/src/unit/engine/PhpunitTestEngine.php
@@ -129,11 +129,13 @@
       substr($file, 0, -4).'Test.php',
     );
 
-    $search = self::getSearchLocationsForTests($path);
+    $search = $this->getSearchLocationsForTests($path);
 
     foreach ($search as $search_path) {
       foreach ($possible_files as $possible_file) {
+
         $full_path = $search_path.$possible_file;
+
         if (!Filesystem::pathExists($full_path)) {
           // If the file doesn't exist, it's clearly a miss.
           continue;
@@ -142,10 +144,12 @@
           // Don't look above the project root.
           continue;
         }
+
         if (0 == strcasecmp(Filesystem::resolvePath($full_path), $path)) {
           // Don't return the original file.
           continue;
         }
+
         return $full_path;
       }
     }
@@ -193,11 +197,16 @@
    * @param   string        PHP file to locate test cases for.
    * @return  list<string>  List of directories to search for tests in.
    */
-  public static function getSearchLocationsForTests($path) {
+  public function getSearchLocationsForTests($path) {
     $file = basename($path);
     $dir  = dirname($path);
 
-    $test_dir_names = array('tests', 'Tests');
+    $test_dir_names = $this->getConfigurationManager()->getConfigFromAnySource(
+        'phpunit_test_dirs');
+
+    if (empty($test_dir_names)) {
+        $test_dir_names = array('tests', 'Tests');
+    }
 
     $try_directories = array();
 
diff --git a/src/unit/engine/__tests__/PHPUnitTestEngineTestCase.php b/src/unit/engine/__tests__/PHPUnitTestEngineTestCase.php
--- a/src/unit/engine/__tests__/PHPUnitTestEngineTestCase.php
+++ b/src/unit/engine/__tests__/PHPUnitTestEngineTestCase.php
@@ -8,6 +8,14 @@
   public function testSearchLocations() {
     $path = '/path/to/some/file/X.php';
 
+    $root = dirname(phutil_get_library_root('arcanist'));
+    $working_copy = ArcanistWorkingCopyIdentity::newFromPath($root);
+    $configuration_manager = new ArcanistConfigurationManager();
+    $configuration_manager->setWorkingCopyIdentity($working_copy);
+
+    $phpunitTestEngine = new PhpunitTestEngine();
+    $phpunitTestEngine->setConfigurationManager($configuration_manager);
+
     $this->assertEqual(
       array(
         '/path/to/some/file/',
@@ -36,7 +44,38 @@
         '/tests/path/to/some/file/',
         '/Tests/path/to/some/file/',
       ),
-      PhpunitTestEngine::getSearchLocationsForTests($path));
+      $phpunitTestEngine->getSearchLocationsForTests($path));
+  }
+
+  public function testConfiguredSearchLocations() {
+    $path = '/path/to/some/file/X.php';
+
+    $root = dirname(phutil_get_library_root('arcanist'));
+    $working_copy = ArcanistWorkingCopyIdentity::newFromPath($root);
+    $configuration_manager = new ArcanistConfigurationManager();
+    $configuration_manager->setWorkingCopyIdentity($working_copy);
+    $configuration_manager->setRuntimeConfig(
+        'phpunit_test_dirs', array('tests/Unit'));
+    $phpunitTestEngine = new PhpunitTestEngine();
+    $phpunitTestEngine->setConfigurationManager($configuration_manager);
+
+    $this->assertEqual(
+      array(
+        '/path/to/some/file/',
+        '/path/to/some/file/tests/Unit/',
+        '/path/to/some/tests/Unit/',
+        '/path/to/tests/Unit/',
+        '/path/tests/Unit/',
+        '/tests/Unit/',
+        '/path/to/tests/Unit/file/',
+        '/path/tests/Unit/some/file/',
+        '/tests/Unit/to/some/file/',
+        '/path/to/some/tests/Unit/file/',
+        '/path/to/tests/Unit/some/file/',
+        '/path/tests/Unit/to/some/file/',
+        '/tests/Unit/path/to/some/file/',
+      ),
+      $phpunitTestEngine->getSearchLocationsForTests($path));
   }
 
 }