refactor stack. Add details to example tests.

components/TTNavStack.tsx

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+import * as React from 'react';
+import { NavigationContainer } from '@react-navigation/native';
+import SettingsComponent from '@/components/Settings';
+import { LanguageSelection } from '@/components/LanguageSelection';
+import { createNativeStackNavigator } from '@react-navigation/native-stack';
+import ConversationThread from '@/components/ConversationThread';
+
+const Stack = createNativeStackNavigator();
+
+export default function TTNavStack() {
+  return (
+    <NavigationContainer>
+      <Stack.Navigator initialRouteName='LanguageSelection'>
+        <Stack.Screen name="LanguageSelection" component={LanguageSelection} />
+        <Stack.Screen name="ConversationThread" component={ConversationThread} />
+        <Stack.Screen name="Settings" component={SettingsComponent} />
+      </Stack.Navigator>
+    </NavigationContainer>
+  );
+}

components/__tests__/index.spec.tsx

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+import React from 'react';
+import { fireEvent, render, screen } from '@testing-library/react-native';
+import { NavigationContainer } from '@react-navigation/native';
+import { createStackNavigator } from '@react-navigation/stack';
+import TTNavStack from '../TTNavStack';
+
+jest.mock('expo-file-system', () => require('./__mocks__/expo-file-system'));
+
+const Stack = createStackNavigator();
+
+describe('Navigation', () => {
+  beforeEach(() => {
+    // Reset the navigation state before each test
+    jest.clearAllMocks();
+  });
+
+  it('Navigates to ConversationThread on language selection', async () => {
+    render(<TTNavStack />);
+    const languageSelectionText = await screen.findByText("Language Selection");
+    fireEvent.press(languageSelectionText);
+    expect(await screen.findByText("Conversation Thread")).toBeOnTheScreen();
+  });
+
+  it('Navigates to Settings on settings selection', async () => {
+    render(<TTNavStack />);
+    const settingsButton = await screen.findByText("Settings");
+    fireEvent.press(settingsButton);
+    expect(await screen.findByText("Settings")).toBeOnTheScreen();
+  });
+});