feat: add Money value object

domain/marketplace/__init__.py

@@ -1,3 +1,4 @@
 from .classified_ad import ClassifiedAd as ClassifiedAd
 from .classified_ad_id import ClassifiedAdId as ClassifiedAdId
+from .money import Money as Money
 from .user_id import UserId as UserId

domain/marketplace/money.py

@@ -0,0 +1,7 @@
+from dataclasses import dataclass
+from decimal import Decimal
+
+
+@dataclass(frozen=True)
+class Money:
+    amount: Decimal

tests/test_money.py

@@ -0,0 +1,24 @@
+from decimal import Decimal
+
+from domain.marketplace.money import Money
+
+
+def test_money_creation():
+    money = Money(amount=Decimal("99.99"))
+    assert money.amount == Decimal("99.99")
+
+
+def test_money_is_immutable():
+    money = Money(amount=Decimal("10.00"))
+
+    try:
+        money.amount = Decimal("20.00")  # type: ignore
+        assert False, "Should have raised FrozenInstanceError"
+    except AttributeError:
+        pass
+
+
+def test_money_equality():
+    money1 = Money(amount=Decimal("50.00"))
+    money2 = Money(amount=Decimal("50.00"))
+    assert money1 == money2