feat(backend): complete modular monolith with ledger, fastapi and websocket

tests/test_ledger.py

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+import pytest
+import pytest_asyncio
+from decimal import Decimal
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
+from app.models.entities import Base, LedgerEntryType
+from app.domains.ledger.service import LedgerService, InsufficientBalanceError
+
+TEST_DATABASE_URL = "sqlite+aiosqlite:///:memory:"
+
+@pytest_asyncio.fixture
+async def test_session():
+    engine = create_async_engine(TEST_DATABASE_URL, echo=False)
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+    session_maker = async_sessionmaker(engine, expire_on_commit=False, class_=AsyncSession)
+    async with session_maker() as session:
+        yield session
+
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.drop_all)
+    await engine.dispose()
+
+@pytest.mark.asyncio
+async def test_ledger_deposit_flow(test_session: AsyncSession):
+    ledger = LedgerService(test_session)
+    user = "0x6cddF384792C77219fc25C454Cfe264757842830"
+
+    # 1. 初始余额为 0
+    bal = await ledger.get_or_create_balance(user)
+    assert bal.available_balance == Decimal("0")
+
+    # 2. 存入 1000 WUSD
+    entry = await ledger.record_deposit(user, Decimal("1000"), "0xtx1")
+    assert entry.entry_type == LedgerEntryType.DEPOSIT
+    assert entry.amount == Decimal("1000")
+    assert entry.balance_after == Decimal("1000")
+
+    bal = await ledger.get_or_create_balance(user)
+    assert bal.available_balance == Decimal("1000")
+
+@pytest.mark.asyncio
+async def test_ledger_trade_and_insufficient_balance(test_session: AsyncSession):
+    ledger = LedgerService(test_session)
+    user = "0x6cddF384792C77219fc25C454Cfe264757842830"
+
+    # 充值 500 WUSD
+    await ledger.record_deposit(user, Decimal("500"), "0xtx1")
+
+    # 尝试买入 600 WUSD (超额报错)
+    with pytest.raises(InsufficientBalanceError):
+        await ledger.record_trade(
+            address=user,
+            market_address="0xmarket1",
+            order_id="order_1",
+            side="BUY",
+            amount=Decimal("600"),
+            fee=Decimal("3.6")
+        )
+
+    # 成功买入 100 WUSD (扣除 100 + 0.6 手续费)
+    entry = await ledger.record_trade(
+        address=user,
+        market_address="0xmarket1",
+        order_id="order_2",
+        side="BUY",
+        amount=Decimal("100"),
+        fee=Decimal("0.6")
+    )
+    assert entry.entry_type == LedgerEntryType.TRADE_BUY
+    assert entry.amount == Decimal("-100.6")
+    assert entry.balance_after == Decimal("399.4")
+
+    # 验证不可变流水历史条数
+    history = await ledger.list_user_ledger(user)
+    assert len(history) == 2