diff --git a/joj3_config_generator/transformers/task.py b/joj3_config_generator/transformers/task.py
index 6fcaa0e..9ecb7a5 100644
--- a/joj3_config_generator/transformers/task.py
+++ b/joj3_config_generator/transformers/task.py
@@ -1,4 +1,3 @@
-import os
 import re
 import shlex
 from functools import partial
@@ -256,7 +255,7 @@ def get_testcases(
 ) -> Set[str]:  # basedir here should be task_conf.root / task_conf.path
     testcases = set()
     for testcases_path in (task_root / task_path).parent.glob("**/*.in"):
-        if not os.path.exists(str(testcases_path).removesuffix(".in") + ".out"):
+        if not testcases_path.with_suffix(".out").exists():
             logger.warning(f"Testcase {testcases_path} has no corresponding .out file")
             continue
         testcases.add(