Fix test_parallel_execution and add a little check on the output

Author: Pierre-Sassoulas

tests/test_self.py

@@ -243,14 +243,19 @@ def test_no_out_encoding(self):
         )
 
     def test_parallel_execution(self):
+        out = StringIO()
         self._runtest(
             [
                 "-j 2",
                 join(HERE, "functional", "a", "arguments.py"),
-                join(HERE, "functional", "a", "arguments.py"),
             ],
+            out=out,
             # We expect similarities to fail and an error
-            code=MSG_TYPES_STATUS["R"] | MSG_TYPES_STATUS["E"],
+            code=MSG_TYPES_STATUS["E"],
+        )
+        assert (
+            "Unexpected keyword argument 'fourth' in function call"
+            in out.getvalue().strip()
         )
 
     def test_parallel_execution_missing_arguments(self):