feat: add equals() to Price and Uuid Value Objects

src/Billing/Shared/Domain/ValueObject/Uuid.ts

@@ -22,4 +22,15 @@ export default abstract class Uuid {
     public toIdentity(): Domain.Identity {
         return this.identity;
     }
+
+    /**
+     * Value Object equality — two UUID-based identities are equal when
+     * they represent the same UUID string value.
+     *
+     * Source: Evans (Blue Book), p. 98 — "Value objects should be
+     * testable for equality."
+     */
+    public equals(other: Uuid): boolean {
+        return this.toString() === other.toString();
+    }
 }

src/Billing/Transaction/Domain/ValueObject/Price.ts

@@ -39,4 +39,15 @@ export default class Price {
         this.amount = amount;
         this.currency = currency;
     }
+
+    /**
+     * Value Object equality — two Price instances are equal when they
+     * represent the same amount in the same currency.
+     *
+     * Source: Evans (Blue Book), p. 98 — "Value objects should be
+     * testable for equality."
+     */
+    public equals(other: Price): boolean {
+        return this.amount === other.amount && this.currency === other.currency;
+    }
 }

tests/Billing/Transaction/Domain/Transaction/ValueObject/Price.test.ts

@@ -13,4 +13,28 @@ describe("Price", () => {
         const todo = () => new Price("12.5", "GBP");
         expect(todo).toThrow(InvalidArgumentException);
     });
+
+    test("Negative amount is rejected", () => {
+        const todo = () => new Price("-1", "EUR");
+        expect(todo).toThrow(InvalidArgumentException);
+    });
+
+    test("Non-numeric amount is rejected", () => {
+        const todo = () => new Price("abc", "EUR");
+        expect(todo).toThrow(InvalidArgumentException);
+    });
+
+    describe("equals", () => {
+        test("two prices with the same amount and currency are equal", () => {
+            expect(new Price("10.00", "EUR").equals(new Price("10.00", "EUR"))).toBe(true);
+        });
+
+        test("prices with different amounts are not equal", () => {
+            expect(new Price("10.00", "EUR").equals(new Price("9.99", "EUR"))).toBe(false);
+        });
+
+        test("prices with different currencies are not equal", () => {
+            expect(new Price("10.00", "EUR").equals(new Price("10.00", "USD"))).toBe(false);
+        });
+    });
 });

tests/Billing/Transaction/Domain/Transaction/ValueObject/TransactionId.test.ts

@@ -0,0 +1,24 @@
+import TransactionId from "@Transaction/Domain/ValueObject/TransactionId";
+
+const UUID_A = "ae081e7a-ec8c-4ff1-9de5-f70383fe03a7";
+const UUID_B = "f47ac10b-58cc-4372-a567-0e02b2c3d479";
+
+describe("TransactionId", () => {
+    test("two ids with the same UUID are equal", () => {
+        expect(new TransactionId(UUID_A).equals(new TransactionId(UUID_A))).toBe(true);
+    });
+
+    test("two ids with different UUIDs are not equal", () => {
+        expect(new TransactionId(UUID_A).equals(new TransactionId(UUID_B))).toBe(false);
+    });
+
+    test("generates a unique id when constructed without value", () => {
+        const a = new TransactionId();
+        const b = new TransactionId();
+        expect(a.equals(b)).toBe(false);
+    });
+
+    test("Invalid UUID is rejected", () => {
+        expect(() => new TransactionId("not-a-uuid")).toThrow();
+    });
+});