Root cause analysis in Testing Fundamentals - Test Execution Trace

Test Overview

This test simulates a simple login functionality check and demonstrates how root cause analysis helps identify the exact reason for a test failure.

Test Code - Selenium

Testing Fundamentals

import unittest
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

class LoginTest(unittest.TestCase):
    def setUp(self):
        self.driver = webdriver.Chrome()
        self.driver.get('https://example.com/login')

    def test_login_with_valid_credentials(self):
        driver = self.driver
        # Wait for username field
        WebDriverWait(driver, 10).until(EC.presence_of_element_located((By.ID, 'username')))
        username_input = driver.find_element(By.ID, 'username')
        username_input.send_keys('validUser')

        # Wait for password field
        WebDriverWait(driver, 10).until(EC.presence_of_element_located((By.ID, 'password')))
        password_input = driver.find_element(By.ID, 'password')
        password_input.send_keys('validPass')

        # Click login button
        login_button = driver.find_element(By.ID, 'loginBtn')
        login_button.click()

        # Wait for welcome message
        welcome_message = WebDriverWait(driver, 10).until(
            EC.presence_of_element_located((By.ID, 'welcomeMsg'))
        )

        self.assertEqual(welcome_message.text, 'Welcome validUser!')

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

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

Execution Trace - 8 Steps

Step	Action	System State	Assertion	Result
1	Test starts and opens Chrome browser	Browser window opens at 'https://example.com/login' page	—	PASS
2	Waits for username input field to be present	Login page loaded with username input visible	Presence of element with ID 'username'	PASS
3	Finds username input and enters 'validUser'	Username field filled with 'validUser'	—	PASS
4	Waits for password input field to be present	Password input field visible on login page	Presence of element with ID 'password'	PASS
5	Finds password input and enters 'validPass'	Password field filled with 'validPass'	—	PASS
6	Finds and clicks the login button	Login button clicked, form submitted	—	PASS
7	Waits for welcome message element to appear	Page attempts to load welcome message with ID 'welcomeMsg'	Presence of element with ID 'welcomeMsg'	FAIL
8	Assertion to check welcome message text 'Welcome validUser!'	No welcome message found, test cannot verify text	welcome_message.text == 'Welcome validUser!'	FAIL

Failure Scenario

Failing Condition: The welcome message element with ID 'welcomeMsg' does not appear after login

Execution Trace Quiz - 3 Questions

At which step did the test first fail?

A Clicking the login button

B Entering the password

C Waiting for the welcome message element

D Opening the browser

Key Result

Root cause analysis helps pinpoint the exact step and reason for failure, enabling focused debugging and faster fixes.

Practice

1. What is the main goal of root cause analysis in software testing?

easy

A. To find the main reason behind a problem

B. To write more test cases quickly

C. To increase the number of bugs found

D. To improve the user interface design

Solution

1. Step 1: Understand the purpose of root cause analysis

   Root cause analysis aims to identify the fundamental reason why a problem occurs.

2. Step 2: Compare options with the purpose

   Only To find the main reason behind a problem matches the goal of finding the main reason behind a problem.

3. Final Answer:

   To find the main reason behind a problem -> Option A

4. Quick Check:

   Root cause analysis = find main reason [OK]

Hint: Root cause analysis = find main problem reason [OK]

Common Mistakes:

• Confusing root cause analysis with test case writing
• Thinking it increases bug count directly
• Mixing it with UI design improvements

2. Which of the following is a correct first step in performing root cause analysis?

easy

A. Fix the bug immediately without investigation

B. Ignore the problem if it is rare

C. Ask 'Why?' repeatedly to dig deeper

D. Write automated tests before analysis

Solution

1. Step 1: Identify the initial action in root cause analysis

   The process starts by asking 'Why?' multiple times to understand the problem deeply.

2. Step 2: Evaluate the options

   Only Ask 'Why?' repeatedly to dig deeper describes this investigative questioning approach correctly.

3. Final Answer:

   Ask 'Why?' repeatedly to dig deeper -> Option C

4. Quick Check:

   Root cause analysis starts with asking 'Why?' [OK]

Hint: Start root cause analysis by asking 'Why?' [OK]

Common Mistakes:

• Trying to fix before understanding the cause
• Ignoring rare problems without analysis
• Confusing test writing with root cause steps

3. Consider this scenario: A test fails because the login button does not respond. After investigation, you find the button's click event is not bound due to a missing script file. What is the root cause?

medium

A. The script file is missing, so click event is not bound

B. The login button is not visible

C. The test case is incorrect

D. The server is down

Solution

1. Step 1: Analyze the failure reason

   The test fails because the login button does not respond to clicks.

2. Step 2: Identify the root cause

   The missing script file causes the click event not to bind, which is the main reason for failure.

3. Final Answer:

   The script file is missing, so click event is not bound -> Option A

4. Quick Check:

   Missing script file = root cause [OK]

Hint: Root cause is the missing script causing failure [OK]

Common Mistakes:

• Blaming the test case instead of the cause
• Assuming UI visibility is the problem
• Incorrectly blaming server downtime

4. You have a failing test due to a timeout error. You suspect the root cause is a slow database query. Which debugging step will best confirm this?

medium

A. Ignore the timeout and rerun the test

B. Check the test script syntax

C. Restart the test environment

D. Run the database query separately and measure time

Solution

1. Step 1: Identify the suspected root cause

   The slow database query is suspected to cause the timeout.

2. Step 2: Choose the debugging action to confirm

   Running the query separately and measuring its time will confirm if it is slow.

3. Final Answer:

   Run the database query separately and measure time -> Option D

4. Quick Check:

   Measure suspected cause to confirm root cause [OK]

Hint: Test suspected cause directly to confirm [OK]

Common Mistakes:

• Checking unrelated test script syntax
• Restarting environment without analysis
• Ignoring the error and rerunning blindly

5. A web app test fails intermittently due to a 'null reference' error. After root cause analysis, you find the error happens only when the user profile data is missing. How should you fix this to prevent future failures?

hard

A. Increase test timeout to avoid failure

B. Add a check in code to handle missing profile data gracefully

C. Remove the user profile feature entirely

D. Ignore the error since it happens rarely

Solution

1. Step 1: Understand the root cause

   The null reference error occurs because the code does not handle missing user profile data.

2. Step 2: Choose the fix to prevent recurrence

   Adding a code check to handle missing data gracefully will stop the error from happening again.

3. Final Answer:

   Add a check in code to handle missing profile data gracefully -> Option B

4. Quick Check:

   Fix root cause by handling missing data [OK]

Hint: Fix root cause by coding safe checks [OK]

Common Mistakes:

• Ignoring rare errors instead of fixing
• Removing features unnecessarily
• Changing unrelated test settings