diff --git a/__tests__/scripts.test.js b/__tests__/scripts.test.js
index 5df2024..b1e9280 100644
--- a/__tests__/scripts.test.js
+++ b/__tests__/scripts.test.js
@@ -20,6 +20,13 @@ jest.mock('../src/solver/glpk.min.js', () => ({
 // Mocking console.log
 const consoleLogMock = jest.spyOn(console, 'log').mockImplementation(() => {});
 
+// Mock useRouter to avoid invariant error
+jest.mock('next/navigation', () => ({
+  useRouter: jest.fn(() => ({
+    push: jest.fn(), // Mock the 'push' function
+  })),
+}));
+
 beforeEach(() => {
     document.body.innerHTML = `
       <div>
@@ -90,7 +97,7 @@ test('calculate_click should display "Calculating" in the output box', () => {
     document.getElementById('bounds').value = 'x <= 5';
     document.getElementById('vars').value = 'x\ny';
 
-    // Simuliere den Button-Klick, der die Berechnung startet
+    // Simulate the button click to trigger calculation
     fireEvent.click(screen.getByText('Calculate'));
 
     // Check the contents of out box
@@ -101,4 +108,3 @@ test('calculate_click should display "Calculating" in the output box', () => {
     mockClear.mockRestore();
     mockLog.mockRestore();
 });
-
diff --git a/src/app/page.tsx b/src/app/page.tsx
index 0b1bb00..994b526 100644
--- a/src/app/page.tsx
+++ b/src/app/page.tsx
@@ -11,7 +11,7 @@ import { LanguageContext } from './context/LanguageContext';
 export default function Home() {
   const { language, setLanguage } = useContext(LanguageContext);
   const [maxminOption, setMaxminOption] = useState('maximize');
-  const [model] = useState('spec');
+  const [model, selectedModel] = useState('spec');
   const router = useRouter();
   
 
@@ -39,9 +39,9 @@ export default function Home() {
   };
 
   const changeModel = (event: React.ChangeEvent<HTMLSelectElement>) => {
-    const selectedModel = event.target.value;
+    selectedModel(event.target.value);
 
-    if (selectedModel === 'gen') {
+    if (event.target.value === 'gen') {
       router.push('./glp');
     }
   };