Fix transfocator timeout error on repeated sets (#1885)

* Replace transfocator observe with short sleep

Author: olliesilvester

src/dodal/devices/beamlines/i04/transfocator.py

@@ -3,7 +3,6 @@
 from ophyd_async.core import (
     AsyncStatus,
     StandardReadable,
-    observe_value,
     wait_for_value,
 )
 from ophyd_async.epics.core import epics_signal_r, epics_signal_rw
@@ -57,16 +56,12 @@ async def set(self, value: float):
         """
         LOGGER.info(f"Transfocator setting {value} beamsize")
 
-        # Logic in the IOC calculates _num_lenses_calc_rbv when _vert_size_calc_sp changes
-
-        # Register an observer before setting _vert_size_calc_sp to ensure we don't miss changes
-        num_lenses_calc_iterator = observe_value(
-            self._num_lenses_calc_rbv, timeout=self.TIMEOUT
-        )
-
-        await anext(num_lenses_calc_iterator)
         await self._vert_size_calc_sp.set(value)
-        calc_lenses = await anext(num_lenses_calc_iterator)
+        # Logic in the IOC calculates _num_lenses_calc_rbv when _vert_size_calc_sp changes,
+        # but this isn't instant so we need a short sleep until
+        # https://jira.diamond.ac.uk/browse/I04-1100
+        await asyncio.sleep(0.1)
+        calc_lenses = await self._num_lenses_calc_rbv.get_value()
 
         async with periodic_reminder(
             f"Waiting for transfocator to insert {calc_lenses} into beam"

tests/devices/beamlines/i04/test_transfocator.py

@@ -18,16 +18,9 @@ def lens_number_is_half_beamsize(
     transfocator._vert_size_calc_sp.subscribe_reading(lens_number_is_half_beamsize)
 
 
-async def set_beamsize_to_same_value_as_mock_signal(
-    transfocator: Transfocator, value: float
-):
-    set_mock_value(transfocator._num_lenses_calc_rbv, value)
-    await transfocator.set(value)
-
-
-@patch("dodal.devices.beamlines.i04.transfocator.wait_for_value")
+@patch("dodal.devices.beamlines.i04.transfocator.asyncio.sleep", new=AsyncMock())
+@patch("dodal.devices.beamlines.i04.transfocator.wait_for_value", new=AsyncMock())
 async def test_when_beamsize_set_then_set_correctly_on_device_and_waited_on(
-    mock_wait_for_value,
     fake_transfocator: Transfocator,
 ):
     given_predicted_lenses_is_half_of_beamsize(fake_transfocator)