Add mock value for slits in bimorph mirror

Author: teoching0705

tests/plans/test_bimorph.py

@@ -87,6 +87,8 @@ def slits(RE: RunEngine) -> Slits:
     for motor in [slits.x_gap, slits.y_gap, slits.x_centre, slits.y_centre]:
         # Set velocity to avoid zero velocity error:
         set_mock_value(motor.velocity, 1)
+        set_mock_value(motor.low_limit_travel, -399.99)
+        set_mock_value(motor.high_limit_travel, -399.99)
 
         def callback(value, wait=False, signal=motor.user_readback):
             set_mock_value(signal, value)