fix test producing unwanted traceback

tests/integration/test_platforms.py

@@ -16,9 +16,14 @@
 """Integration testing for platforms functionality.
 """
 
+from contextlib import suppress
+
+from cylc.flow.exceptions import NoPlatformsError
+from cylc.flow.task_job_logs import get_task_job_activity_log
+
 
 async def test_prep_submit_task_tries_multiple_platforms(
-    flow, scheduler, run, mock_glbl_cfg, monkeypatch
+    flow, scheduler, run, mock_glbl_cfg, monkeypatch, tmp_path
 ):
     """Preparation tries multiple platforms within a group if the
     task platform setting matches a group, and that after all platforms
@@ -43,9 +48,8 @@ async def test_prep_submit_task_tries_multiple_platforms(
     schd = scheduler(wid, paused_start=False, run_mode='live')
     async with run(schd):
         itask = schd.pool.get_tasks()[0]
-        # Avoid breaking on trying to create log file path:
-        schd.task_job_mgr._create_job_log_path = lambda *_: None
+        itask.submit_num = 1
         schd.task_job_mgr.bad_hosts = {'broken', 'broken2'}
         res = schd.task_job_mgr._prep_submit_task_job(schd.workflow, itask)
-        assert res is True
+        assert isinstance(res, NoPlatformsError)
         assert not schd.task_job_mgr.bad_hosts