Verify user login with valid and invalid credentials

Preconditions (1)

Step 1: Enter 'validuser@example.com' in the email input field

Step 2: Enter 'ValidPass123' in the password input field

Step 3: Click the 'Login' button

Step 4: Verify that the user is redirected to the dashboard page

Step 5: Log out to return to the login page

Step 6: Enter 'invaliduser@example.com' in the email input field

Step 7: Enter 'WrongPass' in the password input field

Step 8: Click the 'Login' button

Step 9: Verify that an error message 'Invalid email or password' is displayed

✅ Expected Result: User successfully logs in with valid credentials and sees the dashboard. User cannot log in with invalid credentials and sees the correct error message.

Automation Requirements - Selenium with Python

Assertions Needed:

Verify current URL is dashboard URL after valid login

Verify error message text after invalid login

Best Practices:

Use explicit waits to wait for elements to be visible or clickable

Use meaningful locators like By.ID or By.NAME

Separate test logic and locators for maintainability

Clean up by logging out after valid login test

Automated Solution

Testing Fundamentals

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
import unittest

class TestAuthentication(unittest.TestCase):
    def setUp(self):
        self.driver = webdriver.Chrome()
        self.driver.get('https://example.com/login')
        self.wait = WebDriverWait(self.driver, 10)

    def test_valid_and_invalid_login(self):
        driver = self.driver
        wait = self.wait

        # Valid login
        email_input = wait.until(EC.visibility_of_element_located((By.ID, 'email')))
        email_input.clear()
        email_input.send_keys('validuser@example.com')

        password_input = driver.find_element(By.ID, 'password')
        password_input.clear()
        password_input.send_keys('ValidPass123')

        login_button = driver.find_element(By.ID, 'login-button')
        login_button.click()

        # Wait for dashboard URL
        wait.until(EC.url_contains('/dashboard'))
        self.assertIn('/dashboard', driver.current_url, 'Dashboard URL not loaded after valid login')

        # Log out to return to login page
        logout_button = wait.until(EC.element_to_be_clickable((By.ID, 'logout-button')))
        logout_button.click()

        wait.until(EC.url_contains('/login'))

        # Invalid login
        email_input = wait.until(EC.visibility_of_element_located((By.ID, 'email')))
        email_input.clear()
        email_input.send_keys('invaliduser@example.com')

        password_input = driver.find_element(By.ID, 'password')
        password_input.clear()
        password_input.send_keys('WrongPass')

        login_button = driver.find_element(By.ID, 'login-button')
        login_button.click()

        # Verify error message
        error_message = wait.until(EC.visibility_of_element_located((By.ID, 'error-message')))
        self.assertEqual(error_message.text, 'Invalid email or password', 'Error message text mismatch')

    def tearDown(self):
        self.driver.quit()

if __name__ == '__main__':
    unittest.main()

The setUp method opens the browser and navigates to the login page before each test.

In test_valid_and_invalid_login, we first enter valid credentials and click login. We wait explicitly for the dashboard URL to load and assert the URL contains '/dashboard'.

Then we log out by clicking the logout button and wait to return to the login page.

Next, we enter invalid credentials and click login. We wait for the error message element to appear and assert its text matches the expected error.

The tearDown method closes the browser after the test finishes.

Explicit waits ensure the test waits for elements or page changes before interacting or asserting, making the test stable.

Using IDs for locators keeps selectors simple and reliable.

Common Mistakes - 4 Pitfalls

Using time.sleep() instead of explicit waits

Using brittle XPath locators that depend on page structure

Not clearing input fields before sending keys

Not verifying the correct page or element after login

Bonus Challenge

Now add data-driven testing with 3 different sets of credentials: one valid, two invalid.

Show Hint