Check SPJ stderr output

Author: Mr-Python-in-China

cyaron/graders/testlib_checker.py

@@ -47,6 +47,9 @@ def __call__(self, outs: str, ans: str, ins: str):
                                     stderr=subprocess.PIPE,
                                     text=True,
                                     check=False)
+            if result.stderr.strip() != 'See file to check exit message':
+                raise ValueError("Invalid output from checker: " +
+                                 result.stderr)
             checker_output = result.stdout
 
             result_element = xmlElementTree.fromstring(checker_output)