diff --git a/joj3_config_generator/transformers/task.py b/joj3_config_generator/transformers/task.py
index 249ff2e..6055412 100644
--- a/joj3_config_generator/transformers/task.py
+++ b/joj3_config_generator/transformers/task.py
@@ -1,3 +1,4 @@
+import os
 import re
 import shlex
 from functools import partial
@@ -259,4 +260,7 @@ def get_testcases(
                 testcases_path.relative_to((task_root / task_path).parent)
             ).removesuffix(".in")
         )
+        assert os.path.exists(
+            str(testcases_path).removesuffix(".in") + ".out"
+        ), f"{testcases_path} does not have a corresponding *.out file!"
     return testcases
diff --git a/tests/convert/diff/case0.out b/tests/convert/diff/case0.out
new file mode 100644
index 0000000..e69de29
diff --git a/tests/convert/diff/case1.out b/tests/convert/diff/case1.out
new file mode 100644
index 0000000..e69de29
diff --git a/tests/convert/diff/case2.out b/tests/convert/diff/case2.out
new file mode 100644
index 0000000..e69de29
diff --git a/tests/convert/diff/case3.out b/tests/convert/diff/case3.out
new file mode 100644
index 0000000..e69de29