Raise when thermocycler hold time is unavailable

pylabrobot/thermocycling/opentrons_backend.py

@@ -162,7 +162,10 @@ async def get_block_status(self) -> BlockStatus:
       return BlockStatus.IDLE
 
   async def get_hold_time(self) -> float:
-    return cast(float, self._find_module().get("holdTime", 0.0))
+    hold_time = self._find_module().get("holdTime")
+    if hold_time is None:
+      raise RuntimeError("Hold time is not available. Is a profile running?")
+    return cast(float, hold_time)
 
   async def get_current_cycle_index(self) -> int:
     """Get the zero-based index of the current cycle from the Opentrons API."""

pylabrobot/thermocycling/opentrons_backend_tests.py

@@ -109,3 +109,11 @@ async def test_getters_return_correct_data(self, mock_list_connected_modules):
     # assert await self.thermocycler_backend.get_total_cycle_count() == 10
     assert await self.thermocycler_backend.get_current_step_index() == 0  # 1 - 1 = 0 (zero-based)
     assert await self.thermocycler_backend.get_total_step_count() == 3
+
+  @patch("pylabrobot.thermocycling.opentrons_backend.list_connected_modules")
+  async def test_get_hold_time_raises_if_not_running(self, mock_list_connected_modules):
+    mock_list_connected_modules.return_value = [{"id": "test_id", "data": {}}]
+
+    with self.assertRaises(RuntimeError) as e:
+      await self.thermocycler_backend.get_hold_time()
+    self.assertEqual(str(e.exception), "Hold time is not available. Is a profile running?")

pylabrobot/thermocycling/thermocycler_tests.py

@@ -137,3 +137,17 @@ async def test_is_profile_running_logic(self):
       self.tc.backend.get_total_step_count.return_value = total_steps  # type: ignore
       print(f"Testing with hold={hold}, cycle={cycle}, total_cycles={total_cycles}, ")
       assert await self.tc.is_profile_running() is expected
+
+  async def test_is_profile_running_raises_if_no_profile_running(self):
+    """RuntimeError from get_hold_time should propagate."""
+    self.tc.backend.get_hold_time.side_effect = RuntimeError("No profile is running")  # type: ignore
+
+    with self.assertRaises(RuntimeError):
+      await self.tc.is_profile_running()
+
+  async def test_is_profile_running_preserves_not_implemented_error(self):
+    """Unsupported backends should still surface NotImplementedError."""
+    self.tc.backend.get_hold_time.side_effect = NotImplementedError  # type: ignore
+
+    with self.assertRaises(NotImplementedError):
+      await self.tc.is_profile_running()