Issue 17502: unittest discovery should use self.testLoader
diff --git a/Lib/unittest/main.py b/Lib/unittest/main.py
index 3396bb0..1e001a6 100644
--- a/Lib/unittest/main.py
+++ b/Lib/unittest/main.py
@@ -157,7 +157,10 @@
             self.test = self.testLoader.loadTestsFromNames(self.testNames,
                                                            self.module)
 
-    def _do_discovery(self, argv, Loader=loader.TestLoader):
+    def _do_discovery(self, argv, Loader=None):
+        if Loader is None:
+            Loader = self.testLoader
+
         # handle command line args for test discovery
         self.progName = '%s discover' % self.progName
         import optparse