cover empty exception message branch in run_speed_cascade

tests/test_speed_math.py

@@ -171,6 +171,17 @@ async def test_an_empty_cascade_is_a_failed_result():
     assert result.tier_attempts == []
 
 
+async def test_cascade_records_exception_class_name_when_no_message_provided():
+    async def bad() -> SpeedResult:
+        raise Exception()
+
+    result = await run_speed_cascade([("bad", bad)])
+    assert result.method == "none"
+    assert len(result.tier_attempts) == 1
+    assert result.tier_attempts[0].ok is False
+    assert result.tier_attempts[0].reason == "Exception"
+
+
 async def test_cascade_never_swallows_cancellation():
     import asyncio