Use support.captured_stdout() and move assertions out of context per review

Author: Bolotnyj

Lib/test/test_filecmp.py

@@ -527,12 +527,12 @@ def fake_private_cmp(a, b, sh):
             _ = dc.subdirs
             dc.phase4_closure()
 
-            with patch("sys.stdout", new=io.StringIO()) as mock_stdout:
+            with support.captured_stdout() as mock_stdout:
                 dc.report()
-                output = mock_stdout.getvalue()
-
-                self.assertIn("Common funny cases", output)
-                self.assertIn("Trouble with common files", output)
+            
+            output = mock_stdout.getvalue()
+            self.assertIn("Common funny cases", output)
+            self.assertIn("Trouble with common files", output)
 
 
 if __name__ == "__main__":