Fix language change after run. (#11)

* Fix language change after run.

* Add unit test.

Author: fkdosilovic

src/judge0/submission.py

@@ -271,6 +271,7 @@ def pre_execution_copy(self) -> "Submission":
         new_submission = Submission()
         for attr in REQUEST_FIELDS:
             setattr(new_submission, attr, copy.deepcopy(getattr(self, attr)))
+        new_submission.language = self.language
         return new_submission
 
     def __iter__(self):

tests/test_submission.py

@@ -1,4 +1,5 @@
-from judge0 import Status, Submission, wait
+from judge0 import run, Status, Submission, wait
+from judge0.base_types import LanguageAlias
 
 
 def test_from_json():
@@ -71,3 +72,23 @@ def test_is_done(request):
     wait(client=client, submissions=submission)
 
     assert submission.is_done()
+
+
+def test_language_before_and_after_execution(request):
+    client = request.getfixturevalue("judge0_ce_client")
+    code = """\
+    public class Main {
+        public static void main(String[] args) {
+            System.out.println("Hello World");
+        }
+    }
+    """
+
+    submission = Submission(
+        source_code=code,
+        language=LanguageAlias.JAVA,
+    )
+
+    assert submission.language == LanguageAlias.JAVA
+    submission = run(client=client, submissions=submission)
+    assert submission.language == LanguageAlias.JAVA