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 22:25:28 2015 +0800
@@ -417,9 +417,15 @@
         """
         basename = os.path.basename(full_path)
         if os.path.isfile(full_path):
-            if not VALID_MODULE_NAME.match(basename):
-                # valid Python identifiers only
-                return None, False
+            root, ext = os.path.splitext(basename)
+            try:
+                if not (ext == '.py' and root.isidentifier()):
+                    # valid Python identifiers only
+                    return None, False
+            except:
+                if not VALID_MODULE_NAME.match(basename):
+                    # valid Python identifiers only
+                    return None, False
             if not self._match_path(basename, full_path, pattern):
                 return None, False
             # if the test file matches, load it