diff --git a/tests/simulateTraffic.ts b/scripts/simulate-traffic.ts
similarity index 68%
rename from tests/simulateTraffic.ts
rename to scripts/simulate-traffic.ts
index c10e917..649cca6 100644
--- a/tests/simulateTraffic.ts
+++ b/scripts/simulate-traffic.ts
@@ -1,3 +1,15 @@
+/**
+ * simulate-traffic.ts — manual load test utility
+ *
+ * Fires 500 Create + GetOne requests against a running API server.
+ * Assumes the server is up at http://127.0.0.1:8080.
+ *
+ * Usage:
+ *   npx ts-node scripts/simulate-traffic.ts
+ *
+ * This is NOT a Jest test file. It lives in scripts/ rather than tests/
+ * to avoid polluting Jest discovery and to clarify its purpose.
+ */
 import axios from "axios";
 import { v4 } from "uuid";
 
@@ -8,13 +20,14 @@ async function call() {
         const response = await axios.post("http://127.0.0.1:8080/transaction", {
             price: {
                 amount: Math.floor(Math.random() * (40 - 30)) + 30,
-                currency: "EUR" },
+                currency: "EUR",
+            },
             product: "demo",
             uuid: uuid = v4(),
         });
 
         console.log("Code: ", response.status);
-        console.log(`http://127.1:8080/transaction/${uuid}`);
+        console.log(`http://127.0.0.1:8080/transaction/${uuid}`);
 
         setTimeout(async () => {
             await Promise.all([
@@ -23,7 +36,7 @@ async function call() {
                 axios.get(`http://127.0.0.1:8080/transaction/${uuid}`),
                 axios.get(`http://127.0.0.1:8080/transaction/${uuid}`),
                 axios.get(`http://127.0.0.1:8080/transaction/${uuid}`),
-            ])
+            ]);
          }, 80);
 
     } catch (err) {
diff --git a/tests/Billing/Transaction/Application/UseCase/Transaction/GetOne.test.ts b/tests/Billing/Transaction/Application/UseCase/Transaction/GetOne.test.ts
index 65133f9..c477bc8 100644
--- a/tests/Billing/Transaction/Application/UseCase/Transaction/GetOne.test.ts
+++ b/tests/Billing/Transaction/Application/UseCase/Transaction/GetOne.test.ts
@@ -1,20 +1,26 @@
-import {  Framework } from "hollywood-js";
+import { Framework } from "hollywood-js";
+import * as prom from "prom-client";
 import { getConnectionManager } from "typeorm";
 import {TestKernelFactory} from "../../../../../TestKernelFactory";
 import GetOneQuery from "@Transaction/Application/GetOne/Query";
 import Transaction from "@Transaction/Domain/Transaction";
 import TransactionId from "@Transaction/Domain/ValueObject/TransactionId";
 import Price from "@Transaction/Domain/ValueObject/Price";
+import NotFoundException from "@Shared/Domain/Exceptions/NotFoundException";
 import {InMemoryTransactionRepository} from "../../../Infrastructure/InMemoryRepository";
 
+const EXISTING_UUID = "ae081e7a-ec8c-4ff1-9de5-f70383fe03a7";
+const MISSING_UUID  = "f47ac10b-58cc-4372-a567-0e02b2c3d479";
+
 describe("GetOne Transaction", () => {
     let kernel: Framework.Kernel;
 
     beforeEach(async () => {
+        prom.register.clear();
         kernel = await TestKernelFactory();
         const repository = kernel.container.get<InMemoryTransactionRepository>("domain.transaction.repository");
         await repository.save(Transaction.create(
-            new TransactionId("ae081e7a-ec8c-4ff1-9de5-f70383fe03a7"),
+            new TransactionId(EXISTING_UUID),
             "",
             new Price("1", "EUR"),
         ));
@@ -26,9 +32,15 @@ describe("GetOne Transaction", () => {
 
     test("GetOne a valid transaction", async () => {
         expect.assertions(3);
-        const transaction: any = await kernel.app.ask(new GetOneQuery("ae081e7a-ec8c-4ff1-9de5-f70383fe03a7"));
+        const transaction: any = await kernel.app.ask(new GetOneQuery(EXISTING_UUID));
         expect(transaction).not.toBe(null);
         expect(transaction).not.toBe(undefined);
-        expect(transaction.data.uuid).toBe("ae081e7a-ec8c-4ff1-9de5-f70383fe03a7");
+        expect(transaction.data.uuid).toBe(EXISTING_UUID);
+    });
+
+    test("GetOne a non-existent transaction throws NotFoundException", async () => {
+        expect.assertions(1);
+        await expect(kernel.app.ask(new GetOneQuery(MISSING_UUID)))
+            .rejects.toThrow(NotFoundException);
     });
 });
diff --git a/tests/Billing/Transaction/Domain/Transaction/Transaction.test.ts b/tests/Billing/Transaction/Domain/Transaction/Transaction.test.ts
index 3ee667a..cdbb7f8 100644
--- a/tests/Billing/Transaction/Domain/Transaction/Transaction.test.ts
+++ b/tests/Billing/Transaction/Domain/Transaction/Transaction.test.ts
@@ -3,21 +3,36 @@ import Price from "@Transaction/Domain/ValueObject/Price";
 import TransactionId from "@Transaction/Domain/ValueObject/TransactionId";
 import Transaction from "@Transaction/Domain/Transaction";
 import TransactionWasCreated from "@Transaction/Domain/Events/TransactionWasCreated";
+import InvalidArgumentException from "@Shared/Domain/Exceptions/InvalidArgumentException";
+
+const FIXED_UUID = "ae081e7a-ec8c-4ff1-9de5-f70383fe03a7";
 
 describe("Transaction", () => {
     test("Create transaction", () => {
         const price = new Price("2", "EUR");
-        const transactionID = new TransactionId("ae081e7a-ec8c-4ff1-9de5-f70383fe03a7");
+        const transactionID = new TransactionId(FIXED_UUID);
         const instance = Transaction.create(transactionID, "product", price);
         const stream = instance.getUncommittedEvents();
 
         const event = stream.events[0].event as TransactionWasCreated;
 
-        expect(instance.getAggregateRootId().toString()).toBe("ae081e7a-ec8c-4ff1-9de5-f70383fe03a7");
+        expect(instance.getAggregateRootId().toString()).toBe(FIXED_UUID);
         expect(stream.events[0]).toBeInstanceOf(Domain.DomainMessage);
         expect(event.product).toBe("product");
         expect(event.amount).toBe(price.amount);
         expect(event.currency).toBe(price.currency);
         expect(instance.version()).toBe(0);
     });
+
+    test("Creating a transaction with a negative price is rejected by the domain", () => {
+        const transactionID = new TransactionId(FIXED_UUID);
+        expect(() => Transaction.create(transactionID, "product", new Price("-1", "EUR")))
+            .toThrow(InvalidArgumentException);
+    });
+
+    test("Creating a transaction with an unknown currency is rejected by the domain", () => {
+        const transactionID = new TransactionId(FIXED_UUID);
+        expect(() => Transaction.create(transactionID, "product", new Price("10", "GBP")))
+            .toThrow(InvalidArgumentException);
+    });
 });