diff --git a/src/12-testing/.github/workflows/run-tests.yml b/src/12-testing/.github/workflows/run-tests.yml
new file mode 100644
index 0000000..050b1ff
--- /dev/null
+++ b/src/12-testing/.github/workflows/run-tests.yml
@@ -0,0 +1,44 @@
+name: Run Tests
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  jest-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: 22
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Run Jest tests
+        run: npm test
+
+  deno-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Set up Deno
+        uses: denoland/setup-deno@v1
+        with:
+          deno-version: 2.2.3
+
+      - name: Install dependencies
+        run: deno install
+
+      - name: Run Deno tests
+        run: deno test
\ No newline at end of file
diff --git a/src/12-testing/.gitignore b/src/12-testing/.gitignore
new file mode 100644
index 0000000..b512c09
--- /dev/null
+++ b/src/12-testing/.gitignore
@@ -0,0 +1 @@
+node_modules
\ No newline at end of file
diff --git a/src/12-testing/deno.lock b/src/12-testing/deno.lock
deleted file mode 100644
index ed41a95..0000000
--- a/src/12-testing/deno.lock
+++ /dev/null
@@ -1,35 +0,0 @@
-{
-  "version": "5",
-  "specifiers": {
-    "jsr:@std/assert@*": "1.0.11",
-    "jsr:@std/assert@^1.0.10": "1.0.11",
-    "jsr:@std/internal@^1.0.5": "1.0.5",
-    "jsr:@std/testing@*": "1.0.9"
-  },
-  "jsr": {
-    "@std/assert@1.0.11": {
-      "integrity": "2461ef3c368fe88bc60e186e7744a93112f16fd110022e113a0849e94d1c83c1",
-      "dependencies": [
-        "jsr:@std/internal"
-      ]
-    },
-    "@std/internal@1.0.5": {
-      "integrity": "54a546004f769c1ac9e025abd15a76b6671ddc9687e2313b67376125650dc7ba"
-    },
-    "@std/testing@1.0.9": {
-      "integrity": "9bdd4ac07cb13e7594ac30e90f6ceef7254ac83a9aeaa089be0008f33aab5cd4",
-      "dependencies": [
-        "jsr:@std/assert@^1.0.10"
-      ]
-    }
-  },
-  "workspace": {
-    "packageJson": {
-      "dependencies": [
-        "npm:@types/jest@^29.5.14",
-        "npm:jest@^29.7.0",
-        "npm:ts-jest@^29.3.2"
-      ]
-    }
-  }
-}
diff --git a/src/12-testing/src/deno/user.service.test.ts b/src/12-testing/src/deno/user.service.test.ts
index 10ee5d7..369b151 100644
--- a/src/12-testing/src/deno/user.service.test.ts
+++ b/src/12-testing/src/deno/user.service.test.ts
@@ -17,3 +17,12 @@ Deno.test('getUserById should return a user', async (t) => {
     assertEquals(result, []);
   });
 });
+
+Deno.test('getUserById', () => {
+  const userService = new UserService();
+  userService.addUser('Tilli', 35);
+
+  const result = userService.getUserById(1);
+
+  assertEquals(result, { id: 1, name: 'Tilli', age: 35 });
+});
diff --git a/src/12-testing/src/deno/utis.test.ts b/src/12-testing/src/deno/utils.test.ts
similarity index 63%
rename from src/12-testing/src/deno/utis.test.ts
rename to src/12-testing/src/deno/utils.test.ts
index 30f0e9b..bbef2a2 100644
--- a/src/12-testing/src/deno/utis.test.ts
+++ b/src/12-testing/src/deno/utils.test.ts
@@ -1,3 +1,4 @@
+import { assertEquals } from 'jsr:@std/assert/equals';
 import { assertThrows } from 'jsr:@std/assert/throws';
 import { riskyFunction } from '../utils.ts';
 
@@ -8,3 +9,7 @@ Deno.test('Soll einen Fehler werfen', () => {
     'Wert darf nicht negativ sein!'
   );
 });
+
+Deno.test('Sollte value zurückgeben', () => {
+  assertEquals(riskyFunction(42), 42);
+});