diff --git a/webapp/src/components/loginAndRegistration/AddUser.test.js b/webapp/src/components/loginAndRegistration/AddUser.test.js
index 8cf04089..56cbfb5f 100644
--- a/webapp/src/components/loginAndRegistration/AddUser.test.js
+++ b/webapp/src/components/loginAndRegistration/AddUser.test.js
@@ -1,14 +1,19 @@
 import React from 'react';
-import { render, screen } from '@testing-library/react';
+import { render, screen, fireEvent, waitFor } from '@testing-library/react';
 import AddUser from './AddUser';
-import { BrowserRouter as Router } from 'react-router-dom'; 
+import axios from 'axios';
+import { BrowserRouter as Router } from 'react-router-dom';
 
 // Mocking useTranslation hook
 jest.mock('react-i18next', () => ({
   useTranslation: () => ({ t: key => key }),
 }));
 
+// Mocking axios to simulate an error response
+jest.mock('axios');
+
 describe('<AddUser />', () => {
+
   test('renders the AddUser component', () => {
     render(
       <Router>
@@ -24,6 +29,150 @@ describe('<AddUser />', () => {
     expect(screen.getByText('addUser.login_link')).toBeInTheDocument();
 
   });
+
+  test('displays error message when passwords do not match', () => {
+    render(
+      <Router>
+        <AddUser />
+      </Router>
+    );
+
+    const usernameInput = screen.getByPlaceholderText('addUser.username_placeholder');
+    fireEvent.change(usernameInput, { target: { value: 'username' } });
+
+    const passwordInput = screen.getByPlaceholderText('addUser.password_placeholder');
+    fireEvent.change(passwordInput, { target: { value: '12345678' } });
+
+    const repeatPasswordInput = screen.getByPlaceholderText('addUser.repeat_password_placeholder');
+    fireEvent.change(repeatPasswordInput, { target: { value: '123456789' } });
+
+    const submitButton = screen.getByText('addUser.register_button');
+    fireEvent.click(submitButton);
+
+    expect(screen.getByText('addUser.error_passwords_no_match')).toBeInTheDocument();
+  });
+
+  test('displays error message when spaces in password', () => {
+    render(
+      <Router>
+        <AddUser />
+      </Router>
+    );
+
+    const usernameInput = screen.getByPlaceholderText('addUser.username_placeholder');
+    fireEvent.change(usernameInput, { target: { value: 'username' } });
+
+    const passwordInput = screen.getByPlaceholderText('addUser.password_placeholder');
+    fireEvent.change(passwordInput, { target: { value: '1234 5678' } });
+
+    const repeatPasswordInput = screen.getByPlaceholderText('addUser.repeat_password_placeholder');
+    fireEvent.change(repeatPasswordInput, { target: { value: '1234 5678' } });
+
+    const submitButton = screen.getByText('addUser.register_button');
+    fireEvent.click(submitButton);
+
+    expect(screen.getByText('addUser.error_password_spaces')).toBeInTheDocument();
+  });
+
+  test('displays error message when passwords too short', () => {
+    render(
+      <Router>
+        <AddUser />
+      </Router>
+    );
+
+    const usernameInput = screen.getByPlaceholderText('addUser.username_placeholder');
+    fireEvent.change(usernameInput, { target: { value: 'username' } });
+
+    const passwordInput = screen.getByPlaceholderText('addUser.password_placeholder');
+    fireEvent.change(passwordInput, { target: { value: '1234567' } });
+
+    const repeatPasswordInput = screen.getByPlaceholderText('addUser.repeat_password_placeholder');
+    fireEvent.change(repeatPasswordInput, { target: { value: '1234567' } });
+
+    const submitButton = screen.getByText('addUser.register_button');
+    fireEvent.click(submitButton);
+
+    expect(screen.getByText('addUser.error_password_minimum_length')).toBeInTheDocument();
+  });
+
+  test('displays error message when passwords too long', () => {
+    render(
+      <Router>
+        <AddUser />
+      </Router>
+    );
+
+    const usernameInput = screen.getByPlaceholderText('addUser.username_placeholder');
+    fireEvent.change(usernameInput, { target: { value: 'username' } });
+
+    const passwordInput = screen.getByPlaceholderText('addUser.password_placeholder');
+    fireEvent.change(passwordInput, { target: { value: '01234567890123456789012345678901234567890123456789012345678901234' } });
+
+    const repeatPasswordInput = screen.getByPlaceholderText('addUser.repeat_password_placeholder');
+    fireEvent.change(repeatPasswordInput, { target: { value: '01234567890123456789012345678901234567890123456789012345678901234' } });
+
+    const submitButton = screen.getByText('addUser.register_button');
+    fireEvent.click(submitButton);
+
+    expect(screen.getByText('addUser.error_password_maximum_length')).toBeInTheDocument();
+  });
+
+  test('displays error message when spaces in username', () => {
+    render(
+      <Router>
+        <AddUser />
+      </Router>
+    );
+
+    const usernameInput = screen.getByPlaceholderText('addUser.username_placeholder');
+    fireEvent.change(usernameInput, { target: { value: 'user name' } });
+
+    const passwordInput = screen.getByPlaceholderText('addUser.password_placeholder');
+    fireEvent.change(passwordInput, { target: { value: '12345678' } });
+
+    const repeatPasswordInput = screen.getByPlaceholderText('addUser.repeat_password_placeholder');
+    fireEvent.change(repeatPasswordInput, { target: { value: '12345678' } });
+
+    const submitButton = screen.getByText('addUser.register_button');
+    fireEvent.click(submitButton);
+
+    expect(screen.getByText('addUser.error_username_spaces')).toBeInTheDocument();
+  });
+
+  test('displays error message when username is already in use', async () => {
+
+    // Mock axios post method to simulate response for username already in use
+    axios.post.mockRejectedValue({ response: { data: { error: 'Username already in use' } } });
+
+    render(
+      <Router>
+        <AddUser />
+      </Router>
+    );
+
+    const usernameInput = screen.getByPlaceholderText('addUser.username_placeholder');
+    fireEvent.change(usernameInput, { target: { value: 'existing_user' } });
+
+    const passwordInput = screen.getByPlaceholderText('addUser.password_placeholder');
+    fireEvent.change(passwordInput, { target: { value: '12345678' } });
+
+    const repeatPasswordInput = screen.getByPlaceholderText('addUser.repeat_password_placeholder');
+    fireEvent.change(repeatPasswordInput, { target: { value: '12345678' } });
+
+    const submitButton = screen.getByText('addUser.register_button');
+    fireEvent.click(submitButton);
+
+    // Wait for the asynchronous axios call to be completed
+    await waitFor(() => {
+      expect(screen.getByText('addUser.error_username_in_use')).toBeInTheDocument();
+    });
+
+    // Ensure axios.post is called with the correct data
+    expect(axios.post).toHaveBeenCalledWith(expect.any(String), { username: 'existing_user', password: '12345678' });
+
+  });
+
 });