feat: add max 2 decimal places validation to Money

domain/marketplace/money.py

@@ -6,6 +6,12 @@ from decimal import Decimal
 class Money:
     amount: Decimal
 
+    def __post_init__(self):
+        if self.amount.as_tuple().exponent < -2:
+            raise ValueError(
+                f"Money amount cannot have more than 2 decimal places: {self.amount}"
+            )
+
     def __add__(self, other):
         return Money(self.amount + other.amount)
 

domain/marketplace/price.py

@@ -6,5 +6,6 @@ from domain.marketplace.money import Money
 @dataclass(frozen=True)
 class Price(Money):
     def __post_init__(self):
+        super().__post_init__()
         if self.amount < 0:
             raise ValueError(f"Price cannot be negative: {self.amount}")

tests/test_money.py

@@ -37,3 +37,26 @@ def test_money_substract():
     money1 = Money(amount=Decimal("5.00"))
     money2 = Money(amount=Decimal("3.00"))
     assert (money1 - money2) == Money(amount=Decimal("2.00"))
+
+
+def test_money_can_not_have_more_than_two_decimals():
+    try:
+        Money(amount=Decimal("1.234"))
+        assert False, "Should have raised ValueError"
+    except ValueError:
+        pass
+
+
+def test_money_allows_two_decimals():
+    money = Money(amount=Decimal("1.23"))
+    assert money.amount == Decimal("1.23")
+
+
+def test_money_allows_one_decimal():
+    money = Money(amount=Decimal("1.2"))
+    assert money.amount == Decimal("1.2")
+
+
+def test_money_allows_no_decimals():
+    money = Money(amount=Decimal(1))
+    assert money.amount == Decimal(1)