Screenshot on failure in Selenium Python - Build an Automation Script

Capture screenshot when login fails

Preconditions (2)

Step 1: Enter '[e-mail]' in the email input field with id 'email'

Step 2: Enter 'wrongpassword' in the password input field with id 'password'

Step 3: Click the login button with id 'loginBtn'

Step 4: Wait for the error message with id 'errorMsg' to appear

✅ Expected Result: Login fails, error message is displayed, and a screenshot of the page is saved

Automation Requirements - selenium

Assertions Needed:

Verify that the error message element with id 'errorMsg' is visible

Verify that a screenshot file is saved when the test fails

Best Practices:

Use explicit waits to wait for elements

Use try-except blocks to catch failures and take screenshots

Use meaningful element locators like IDs

Save screenshots with timestamped filenames

Automated Solution

Selenium Python

import unittest
import time
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
from selenium.common.exceptions import TimeoutException

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

    def test_invalid_login_screenshot_on_failure(self):
        driver = self.driver
        try:
            email_input = self.wait.until(EC.presence_of_element_located((By.ID, 'email')))
            email_input.clear()
            email_input.send_keys('[e-mail]')

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

            login_button = driver.find_element(By.ID, 'loginBtn')
            login_button.click()

            # Wait for error message
            error_msg = self.wait.until(EC.visibility_of_element_located((By.ID, 'errorMsg')))

            # Assert error message is displayed
            self.assertTrue(error_msg.is_displayed(), 'Error message should be visible')

        except (AssertionError, TimeoutException) as e:
            timestamp = time.strftime('%Y%m%d-%H%M%S')
            screenshot_name = f'screenshot_failure_{timestamp}.png'
            driver.save_screenshot(screenshot_name)
            raise e

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

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

This test uses unittest and Selenium WebDriver for Python.

setUp: Opens the browser and navigates to the login page.

test_invalid_login_screenshot_on_failure: Enters invalid credentials, clicks login, and waits for the error message.

If the error message is not visible or any assertion fails, it catches the exception, takes a screenshot with a timestamped filename, and then re-raises the error to fail the test.

tearDown: Closes the browser after the test.

This approach ensures that if the test fails, you get a screenshot to help understand what went wrong.

Common Mistakes - 4 Pitfalls

Using time.sleep() instead of explicit waits

Not catching exceptions to take screenshots on failure

Using brittle locators like absolute XPath

Saving screenshots with fixed filenames

Bonus Challenge

Now add data-driven testing with 3 different invalid login inputs to verify screenshots on each failure

Show Hint

Practice

1. What is the main purpose of taking a screenshot on test failure in Selenium?

easy

A. To capture the current state of the web page for debugging

B. To speed up the test execution

C. To improve the browser's performance

D. To automatically fix the test errors

Solution

1. Step 1: Understand the role of screenshots in testing

   Screenshots help testers see what the user saw when the test failed.

2. Step 2: Identify the purpose of capturing screenshots on failure

   They provide visual evidence to debug UI problems quickly.

3. Final Answer:

   To capture the current state of the web page for debugging -> Option A

4. Quick Check:

   Screenshot on failure = capture page state [OK]

Hint: Screenshots show what failed looks like visually [OK]

Common Mistakes:

• Thinking screenshots speed up tests
• Believing screenshots fix errors automatically
• Confusing screenshots with performance tools

2. Which of the following is the correct syntax to take a screenshot in Selenium Python when a test fails?

easy

A. driver.save_screenshot('error.png')

B. driver.takeScreenshot('error.png')

C. driver.capture('error.png')

D. driver.screenshotSave('error.png')

Solution

1. Step 1: Recall Selenium Python screenshot method

   The correct method to save a screenshot is save_screenshot().

2. Step 2: Verify method names and syntax

   Only driver.save_screenshot('error.png') matches Selenium's API.

3. Final Answer:

   driver.save_screenshot('error.png') -> Option A

4. Quick Check:

   Correct method name = save_screenshot [OK]

Hint: Remember method is save_screenshot with underscore [OK]

Common Mistakes:

• Using camelCase instead of snake_case
• Using non-existent methods like capture or screenshotSave
• Missing parentheses or quotes

3. What will be the output if the following Selenium Python code runs and the element is not found?

try:
    driver.find_element(By.ID, 'submit').click()
except Exception as e:
    driver.save_screenshot('fail.png')
    print('Screenshot saved on failure')

medium

A. No output, test passes silently

B. RuntimeError without screenshot

C. SyntaxError due to missing import

D. Screenshot saved on failure

Solution

1. Step 1: Analyze try-except behavior on element not found

   If element is missing, exception triggers except block.

2. Step 2: Check actions in except block

   Screenshot is saved and message printed: 'Screenshot saved on failure'.

3. Final Answer:

   Screenshot saved on failure -> Option D

4. Quick Check:

   Exception triggers screenshot and print [OK]

Hint: Exception triggers except block actions [OK]

Common Mistakes:

• Assuming test passes silently on failure
• Confusing syntax errors with runtime exceptions
• Ignoring the print statement inside except

4. Identify the error in this Selenium Python snippet intended to save a screenshot on failure:

try:
    driver.find_element(By.NAME, 'login').click()
except:
    driver.save_screenshot(failure.png)

medium

A. No error, code is correct

B. Incorrect exception handling syntax

C. Missing quotes around filename in save_screenshot

D. Wrong method name saveScreenshot instead of save_screenshot

Solution

1. Step 1: Check save_screenshot argument syntax

   Filename must be a string in quotes, but here it is unquoted.

2. Step 2: Confirm exception handling and method name

   Except syntax and method name are correct; only filename is wrong.

3. Final Answer:

   Missing quotes around filename in save_screenshot -> Option C

4. Quick Check:

   Filename must be a string in quotes [OK]

Hint: Always put filename in quotes for save_screenshot [OK]

Common Mistakes:

• Forgetting quotes around filename string
• Changing method name incorrectly
• Misusing except syntax

5. You want to automatically take a screenshot only when a Selenium test fails and save it with a timestamp. Which approach below correctly implements this in Python?

hard

A. Use driver.save_screenshot('fail.png') outside try-except block

B. Use try-except around test steps, call driver.save_screenshot(f"fail_{time.time()}.png") in except

C. Call driver.save_screenshot() before every test step unconditionally

D. Use a loop to retry test steps and save screenshot on success

Solution

1. Step 1: Understand when to take screenshots

   Screenshots should be taken only on failure, inside except block.

2. Step 2: Use timestamp for unique filenames

   Using time.time() in filename ensures unique screenshot names.

3. Final Answer:

   Use try-except around test steps, call driver.save_screenshot(f"fail_{time.time()}.png") in except -> Option B

4. Quick Check:

   Screenshot on failure with timestamp = try-except + formatted filename [OK]

Hint: Take screenshots only in except block with timestamped names [OK]

Common Mistakes:

• Taking screenshots before test steps always
• Saving screenshots outside exception handling
• Retrying tests without capturing failure screenshots