feat: add Price value object extending Money

tests/test_price.py

@@ -0,0 +1,31 @@
+from decimal import Decimal
+
+import pytest
+
+from domain.marketplace.price import Price
+
+
+def test_price_creation():
+    price = Price(amount=Decimal("99.99"))
+    assert price.amount == Decimal("99.99")
+
+
+def test_price_is_immutable():
+    price = Price(amount=Decimal("10.00"))
+
+    try:
+        price.amount = Decimal("20.00")  # type: ignore
+        assert False, "Should have raised FrozenInstanceError"
+    except AttributeError:
+        pass
+
+
+def test_price_can_not_be_negative():
+    with pytest.raises(ValueError):
+        Price(amount=Decimal("-10.00"))
+
+
+def test_price_equality():
+    price1 = Price(amount=Decimal("50.00"))
+    price2 = Price(amount=Decimal("50.00"))
+    assert price1 == price2