diff -r 44253ce374fc Lib/unittest/loader.py
--- a/Lib/unittest/loader.py	Mon Jun 22 12:31:24 2015 -0400
+++ b/Lib/unittest/loader.py	Tue Jun 23 11:45:31 2015 +0800
@@ -17,7 +17,7 @@
 # what about .pyc (etc)
 # we would need to avoid loading the same tests multiple times
 # from '.py', *and* '.pyc'
-VALID_MODULE_NAME = re.compile(r'[_a-z]\w*\.py$', re.IGNORECASE)
+VALID_MODULE_NAME = re.compile(r'[^\W\d]\w*\.py$', re.IGNORECASE)
 
 
 class _FailedTest(case.TestCase):