test: add unit tests for models, payout logic, and room lock

- test_models.py: 10 tests for Room/Horse/Bet/RaceResult dataclasses
- test_payout_logic.py: 12 tests for payout formula (max+round)
- test_room_store_lock.py: 5 tests for get_lock() setdefault pattern
- All 34 tests pass in 0.27s

tests/test_models.py

@@ -0,0 +1,158 @@
+"""Test models.py dataclasses - direct import bypassing __init__.py.
+
+Uses importlib.util to load models.py directly, avoiding nonebot dependency.
+"""
+import pytest
+import importlib.util
+import sys
+from pathlib import Path
+from datetime import datetime
+
+# Load models.py directly without triggering __init__.py
+project_root = Path(__file__).parent.parent
+models_path = project_root / "danding_bot" / "plugins" / "group_horse_racing" / "models.py"
+
+spec = importlib.util.spec_from_file_location("models", models_path)
+models = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(models)
+
+RoomState = models.RoomState
+HorseState = models.HorseState
+Horse = models.Horse
+Bet = models.Bet
+Room = models.Room
+RaceResult = models.RaceResult
+
+
+class TestEnums:
+    def test_room_states(self):
+        assert RoomState.WAITING.value == "waiting"
+        assert RoomState.RUNNING.value == "running"
+        assert RoomState.FINISHED.value == "finished"
+        assert RoomState.INTERRUPTED.value == "interrupted"
+
+    def test_horse_states(self):
+        assert HorseState.READY.value == "ready"
+        assert HorseState.RACING.value == "racing"
+        assert HorseState.FINISHED.value == "finished"
+
+    def test_room_state_string_enum(self):
+        """RoomState is str enum, should work in string comparisons"""
+        assert RoomState.WAITING == "waiting"
+
+    def test_horse_state_string_enum(self):
+        assert HorseState.READY == "ready"
+
+
+class TestHorseDataclass:
+    def test_default_construction(self):
+        h = Horse(owner_id="u1", name="闪电")
+        assert h.owner_id == "u1"
+        assert h.name == "闪电"
+        assert h.position == 0.0
+        assert h.state == HorseState.READY
+        assert h.index == 0
+
+    def test_custom_values(self):
+        h = Horse(owner_id="u2", name="旋风", index=3, position=5.5, state=HorseState.RACING)
+        assert h.index == 3
+        assert h.position == 5.5
+        assert h.state == HorseState.RACING
+
+    def test_finished_state(self):
+        h = Horse(owner_id="u3", name="飞龙", state=HorseState.FINISHED, position=100.0)
+        assert h.state == HorseState.FINISHED
+
+
+class TestBetDataclass:
+    def test_construction(self):
+        b = Bet(user_id="u1", horse_name="闪电", amount=100)
+        assert b.user_id == "u1"
+        assert b.horse_name == "闪电"
+        assert b.amount == 100
+
+    def test_zero_bet(self):
+        b = Bet(user_id="u2", horse_name="旋风", amount=0)
+        assert b.amount == 0
+
+    def test_negative_bet_boundary(self):
+        """Negative bet shouldn't happen but dataclass allows it"""
+        b = Bet(user_id="u3", horse_name="x", amount=-50)
+        assert b.amount == -50
+
+
+class TestRoomDataclass:
+    def test_default_room(self):
+        r = Room(scope="test_group")
+        assert r.scope == "test_group"
+        assert r.state == RoomState.WAITING
+        assert r.horses == {}
+        assert r.bets == []
+        assert r.champion_name is None
+        assert r.tick_count == 0
+        assert r.next_horse_index == 1
+        assert isinstance(r.created_at, datetime)
+
+    def test_room_with_horses(self):
+        r = Room(
+            scope="g1",
+            horses={"闪电": Horse(owner_id="u1", name="闪电")}
+        )
+        assert "闪电" in r.horses
+        assert len(r.horses) == 1
+
+    def test_room_state_transitions(self):
+        r = Room(scope="g1")
+        assert r.state == RoomState.WAITING
+        r.state = RoomState.RUNNING
+        assert r.state == RoomState.RUNNING
+        r.state = RoomState.FINISHED
+        assert r.state == RoomState.FINISHED
+
+    def test_independent_rooms_have_independent_horses(self):
+        """Verify dict default_factory creates independent instances"""
+        r1 = Room(scope="g1")
+        r2 = Room(scope="g2")
+        r1.horses["test"] = Horse(owner_id="u1", name="test")
+        assert "test" not in r2.horses
+
+    def test_independent_rooms_have_independent_bets(self):
+        r1 = Room(scope="g1")
+        r2 = Room(scope="g2")
+        r1.bets.append(Bet(user_id="u1", horse_name="x", amount=10))
+        assert len(r2.bets) == 0
+
+
+class TestRaceResultDataclass:
+    def test_basic_construction(self):
+        rr = RaceResult(
+            race_id="race1",
+            scope="g1",
+            champion_name="闪电",
+            champion_owner="u1",
+            participants=["u1", "u2"],
+            bet_distribution={"u1": 100, "u2": 50},
+            duration_ticks=30,
+            completed_at=datetime.now(),
+        )
+        assert rr.race_id == "race1"
+        assert rr.champion_name == "闪电"
+        assert len(rr.participants) == 2
+        assert rr.point_changes == {}
+        assert rr.point_change_summaries == {}
+
+    def test_with_point_changes(self):
+        rr = RaceResult(
+            race_id="race2",
+            scope="g1",
+            champion_name="旋风",
+            champion_owner="u2",
+            participants=["u1", "u2"],
+            bet_distribution={"u1": 100},
+            duration_ticks=25,
+            completed_at=datetime.now(),
+            point_changes={"u1": -100, "u2": 200},
+            point_change_summaries={"u1": "-100", "u2": "+200"},
+        )
+        assert rr.point_changes["u2"] == 200
+        assert rr.point_change_summaries["u1"] == "-100"