tests: use subTest in test_unparse.test_files

diff --git a/Lib/test/test_tools/test_unparse.py b/Lib/test/test_tools/test_unparse.py
index 517f2613aa023323a38177c8a212c4a79c492a44..ed0001a15af52da0719d91919cfcfddc44d0471a 100644 (file)
--- a/Lib/test/test_tools/test_unparse.py
+++ b/Lib/test/test_tools/test_unparse.py
@@ -293,8 +293,9 @@ class DirectoryTestCase(ASTTestCase):
                     print(f'Skipping {filename}: see issue 27921')
                 continue
 
-            source = read_pyfile(filename)
-            self.check_roundtrip(source)
+            with self.subTest(filename=filename):
+                source = read_pyfile(filename)
+                self.check_roundtrip(source)
 
 
 if __name__ == '__main__':