addressed review comments

api/src/opentrons/protocol_api/_liquid.py

@@ -65,7 +65,7 @@ class LiquidClass:
     def create(cls, liquid_class_definition: LiquidClassSchemaV1) -> "LiquidClass":
         """Liquid class factory method."""
 
-        return LiquidClass(
+        return cls(
             _name=liquid_class_definition.liquidClassName,
             _display_name=liquid_class_definition.displayName,
             _by_pipette_setting=liquid_class_definition.byPipette,

api/src/opentrons/protocol_api/core/engine/protocol.py

@@ -2,6 +2,8 @@
 from __future__ import annotations
 from typing import Dict, Optional, Type, Union, List, Tuple, TYPE_CHECKING
 
+from opentrons_shared_data.liquid_classes import LiquidClassDefinitionDoesNotExist
+
 from opentrons.protocol_engine import commands as cmd
 from opentrons.protocol_engine.commands import LoadModuleResult
 from opentrons_shared_data.deck.types import DeckDefinitionV5, SlotDefV3
@@ -764,8 +766,8 @@ def define_liquid_class(self, name: str) -> LiquidClass:
                 # Calling this often will degrade protocol execution performance.
                 liquid_class_def = liquid_classes.load_definition(name)
                 self._defined_liquid_class_defs_by_name[name] = liquid_class_def
-            except KeyError:
-                raise ValueError("Liquid class definition not found")
+            except LiquidClassDefinitionDoesNotExist:
+                raise ValueError(f"Liquid class definition not found for '{name}'.")
 
         return LiquidClass.create(liquid_class_def)
 

api/tests/opentrons/protocol_api_integration/test_liquid_classes.py

@@ -37,7 +37,10 @@ def test_liquid_class_creation_and_property_fetching(
         == 100
     )
 
-    with pytest.raises(ValueError):
+    with pytest.raises(
+        ValueError,
+        match="No properties found for p300_multi in fixture_glycerol50 liquid class",
+    ):
         glycerol_50.get_for(pipette_right.name, tiprack.load_name)
 
     with pytest.raises(AttributeError):
@@ -46,6 +49,9 @@ def test_liquid_class_creation_and_property_fetching(
     with pytest.raises(AttributeError):
         glycerol_50.display_name = "bar"  # type: ignore
 
+    with pytest.raises(ValueError, match="Liquid class definition not found"):
+        protocol_context.define_liquid_class("non-existent-liquid")
+
 
 def test_liquid_class_feature_flag() -> None:
     """It should raise a not implemented error without the allowLiquidClass flag set."""

shared-data/python/opentrons_shared_data/liquid_classes/__init__.py

@@ -6,7 +6,7 @@
 
 
 class LiquidClassDefinitionDoesNotExist(Exception):
-    """Specified liquid class' definition does not exist."""
+    """Specified liquid class definition does not exist."""
 
 
 # TODO (spp, 2024-10-16): update the path once definitions are added