Performance metrics collection in Selenium Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of collecting performance metrics in Selenium tests?

Performance metrics help measure how fast and efficiently a web page or application loads and runs during automated tests.

beginner

Which Selenium method allows you to access browser performance data?

You can use the execute_script method to run JavaScript that accesses the browser's window.performance API.

intermediate

Name two common performance metrics you can collect from the browser's performance API.

Two common metrics are navigationStart (when navigation started) and loadEventEnd (when page load finished).

intermediate

How can you measure page load time using Selenium and performance timing?

By subtracting navigationStart from loadEventEnd using JavaScript executed in Selenium, you get the total page load time in milliseconds.

beginner

Why is it important to collect performance metrics during automated testing?

Collecting metrics helps identify slow parts of a website, improve user experience, and ensure the app meets speed requirements.

Which Selenium method is used to run JavaScript for performance data?

A click

B find_element

C execute_script

D get

The execute_script method runs JavaScript in the browser context, allowing access to performance data.

What does the performance timing property navigationStart represent?

A When the page finished loading

B When navigation to the page started

C When the first byte was received

D When the DOM was fully parsed

navigationStart marks the time when the browser started navigating to the page.

How do you calculate total page load time from performance timing?

A domComplete - domLoading

B navigationStart - loadEventEnd

C responseEnd - requestStart

D loadEventEnd - navigationStart

Subtracting navigationStart from loadEventEnd gives the total page load time.

Why collect performance metrics during Selenium tests?

A To measure page speed and responsiveness

B To check page content correctness

C To find broken links

D To test user login

Performance metrics help measure how fast and responsive the page is during tests.

Which API provides performance timing data in the browser?

A window.performance

B document.cookie

C navigator.geolocation

D window.localStorage

window.performance API gives access to detailed timing data about page load.

Explain how to collect and calculate page load time using Selenium and browser performance API.

Think about running JavaScript inside Selenium to get timing data.

Why is monitoring performance metrics important in automated web testing?

Consider how speed affects users and quality.

Practice

1. What is the main purpose of collecting performance metrics in Selenium tests?

easy

A. To check if the page layout matches the design

B. To verify the correctness of form inputs

C. To measure how fast a web page and its resources load

D. To test user login functionality

Solution

1. Step 1: Understand performance metrics

   Performance metrics focus on timing data related to page loading and resource fetching.

2. Step 2: Identify the purpose in Selenium context

   In Selenium, performance metrics help measure loading speed, not layout or input correctness.

3. Final Answer:

   To measure how fast a web page and its resources load -> Option C

4. Quick Check:

   Performance metrics = loading speed [OK]

Hint: Performance metrics = page and resource load times [OK]

Common Mistakes:

• Confusing performance metrics with UI layout checks
• Thinking performance metrics test form validation
• Assuming performance metrics check user actions

2. Which Selenium Python code snippet correctly executes JavaScript to get the navigation start time from the performance object?

easy

A. driver.execute_script('return window.performance.timing.navigationStart;')

B. driver.execute_script('window.performance.navigationStart')

C. driver.execute_script('return window.performance.navigationStart')

D. driver.execute_script('window.performance.timing.navigationStart')

Solution

1. Step 1: Identify correct JavaScript property

   The navigation start time is under window.performance.timing.navigationStart.

2. Step 2: Check correct Selenium syntax

   Use return keyword and full property path with semicolon for valid JS execution.

3. Final Answer:

   driver.execute_script('return window.performance.timing.navigationStart;') -> Option A

4. Quick Check:

   Correct JS property and return statement = driver.execute_script('return window.performance.timing.navigationStart;') [OK]

Hint: Use full path with return and semicolon in execute_script [OK]

Common Mistakes:

• Omitting 'return' keyword in execute_script
• Using wrong property path without 'timing'
• Missing semicolon causing JS errors

3. Given the following Selenium Python code snippet, what will be the output if navigationStart is 1000 and loadEventEnd is 3500?

nav_start = driver.execute_script('return window.performance.timing.navigationStart;')
load_end = driver.execute_script('return window.performance.timing.loadEventEnd;')
load_time = load_end - nav_start
print(load_time)

medium

A. 2500

B. 4500

C. 3500

D. 1000

Solution

1. Step 1: Understand the variables

   nav_start = 1000, load_end = 3500 as given.

2. Step 2: Calculate load_time

   load_time = load_end - nav_start = 3500 - 1000 = 2500.

3. Final Answer:

   2500 -> Option A

4. Quick Check:

   3500 - 1000 = 2500 [OK]

Hint: Subtract navigationStart from loadEventEnd for load time [OK]

Common Mistakes:

• Adding instead of subtracting timestamps
• Using wrong variable names
• Confusing loadEventEnd with other timing values

4. Identify the error in this Selenium Python code snippet for collecting page load time:

nav_start = driver.execute_script('return window.performance.timing.navigationStart')
load_end = driver.execute_script('return window.performance.timing.loadEventEnd')
load_time = nav_start - load_end
print(load_time)

medium

A. Variables nav_start and load_end are not defined

B. Missing semicolons in JavaScript cause syntax error

C. Using 'driver.execute_script' is incorrect for performance data

D. The subtraction order is reversed, causing negative load time

Solution

1. Step 1: Check subtraction logic

   Load time should be load_end - nav_start, not nav_start - load_end.

2. Step 2: Understand impact of reversed subtraction

   Reversed order results in negative load time, which is incorrect.

3. Final Answer:

   The subtraction order is reversed, causing negative load time -> Option D

4. Quick Check:

   Correct subtraction order = load_end - nav_start [OK]

Hint: Subtract navigationStart from loadEventEnd, not vice versa [OK]

Common Mistakes:

• Reversing subtraction causing negative results
• Assuming missing semicolons cause errors in this context
• Thinking execute_script can't get performance data

5. You want to collect multiple performance metrics in Selenium Python: navigationStart, responseStart, and loadEventEnd. Which code snippet correctly collects these and calculates the total load time from navigationStart to loadEventEnd?

hard

A. nav = driver.execute_script('window.performance.timing.navigationStart')
resp = driver.execute_script('window.performance.timing.responseStart')
load = driver.execute_script('window.performance.timing.loadEventEnd')
total_load = resp - nav
print(total_load)

B. nav = driver.execute_script('return window.performance.timing.navigationStart;')
resp = driver.execute_script('return window.performance.timing.responseStart;')
load = driver.execute_script('return window.performance.timing.loadEventEnd;')
total_load = load - nav
print(total_load)

C. nav = driver.execute_script('return window.performance.navigationStart;')
resp = driver.execute_script('return window.performance.responseStart;')
load = driver.execute_script('return window.performance.loadEventEnd;')
total_load = load - nav
print(total_load)

D. nav = driver.execute_script('return window.performance.timing.navigationStart;')
resp = driver.execute_script('return window.performance.timing.responseStart;')
load = driver.execute_script('return window.performance.timing.loadEventEnd;')
total_load = resp - load
print(total_load)

Solution

1. Step 1: Verify JavaScript property paths

   Performance timing properties are under window.performance.timing with return keyword.

2. Step 2: Check calculation logic

   Total load time is loadEventEnd minus navigationStart, so load - nav is correct.

3. Final Answer:

   nav = driver.execute_script('return window.performance.timing.navigationStart;') resp = driver.execute_script('return window.performance.timing.responseStart;') load = driver.execute_script('return window.performance.timing.loadEventEnd;') total_load = load - nav print(total_load) -> Option B

4. Quick Check:

   Correct property path and subtraction order = nav = driver.execute_script('return window.performance.timing.navigationStart;') resp = driver.execute_script('return window.performance.timing.responseStart;') load = driver.execute_script('return window.performance.timing.loadEventEnd;') total_load = load - nav print(total_load) [OK]

Hint: Use full timing path and subtract navigationStart from loadEventEnd [OK]

Common Mistakes:

• Using wrong property paths without 'timing'
• Calculating load time with wrong subtraction order
• Omitting 'return' in execute_script calls