Network log capture in Selenium Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Selenium network log capture code?

Consider the following Python Selenium code snippet that captures network logs using Chrome DevTools Protocol (CDP). What will be printed by the last print statement?

Selenium Python

from selenium import webdriver
from selenium.webdriver.chrome.service import Service
from selenium.webdriver.chrome.options import Options
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities

options = Options()
options.add_argument('--headless=new')

caps = DesiredCapabilities.CHROME.copy()
caps['goog:loggingPrefs'] = {'performance': 'ALL'}

service = Service()
driver = webdriver.Chrome(service=service, options=options, desired_capabilities=caps)

driver.get('https://example.com')

logs = driver.get_log('performance')

count = 0
for entry in logs:
    message = entry['message']
    if 'Network.responseReceived' in message:
        count += 1

print(count)
driver.quit()

A Raises a WebDriverException because DesiredCapabilities is deprecated

B Prints the number of network responses received during page load, typically a positive integer like 5 or more

C Raises a KeyError because 'message' key does not exist in log entries

D Prints 0 because 'performance' logs are not enabled by default

💡 Hint

Check how performance logging is enabled and what keys exist in the log entries.

The code enables performance logging via DesiredCapabilities and captures network events. Each log entry has a 'message' key containing JSON strings. Filtering for 'Network.responseReceived' counts network responses. This count is printed as a positive integer.

❓ assertion

intermediate

Which assertion correctly verifies a network request URL in Selenium logs?

You have captured performance logs in Selenium and want to assert that a request to 'https://api.example.com/data' was made. Which assertion code snippet correctly checks this?

Selenium Python

logs = driver.get_log('performance')
urls = []
for entry in logs:
    message = json.loads(entry['message'])['message']
    if message['method'] == 'Network.requestWillBeSent':
        urls.append(message['params']['request']['url'])

A assert any('https://api.example.com/data' in url for url in urls)

B assert 'https://api.example.com/data' in urls

C assert all('https://api.example.com/data' == url for url in urls)

D assert urls.index('https://api.example.com/data') > 0

💡 Hint

Check how to verify if at least one URL matches the target string.

Option A uses any() to check if the target URL is contained in any captured URL, which is correct. Option A checks exact membership which may fail if URLs have query parameters. Option A requires all URLs to match exactly, which is wrong. Option A raises ValueError if URL not found.

🔧 Debug

advanced

Why does this Selenium network log capture code raise a JSONDecodeError?

This code snippet tries to parse network logs but raises json.decoder.JSONDecodeError. Identify the cause.

Selenium Python

import json
logs = driver.get_log('performance')
for entry in logs:
    message = json.loads(entry['message'])
    print(message['message']['method'])

A entry['message'] is a string containing nested JSON; json.loads parses only the outer string, inner 'message' is still a string, causing error

B entry['message'] is not a valid JSON string, causing JSONDecodeError

C driver.get_log('performance') returns empty list, so loop never runs and error is elsewhere

D json module is not imported correctly, causing JSONDecodeError

💡 Hint

Check the structure of the 'message' field in performance logs.

The 'message' field is a JSON string that contains another JSON string inside the 'message' key. The code parses only once, so message['message'] is still a string, not a dict. Accessing ['method'] on a string causes JSONDecodeError or TypeError.

❓ framework

advanced

Which Selenium WebDriver setup correctly enables network log capture with Chrome in Python?

Select the code snippet that correctly configures Chrome WebDriver to capture network logs using performance logging.

A

from selenium import webdriver
from selenium.webdriver.chrome.service import Service

service = Service()
driver = webdriver.Chrome(service=service)
driver.execute_cdp_cmd('Network.enable', {})

B

from selenium import webdriver
from selenium.webdriver.chrome.options import Options

options = Options()
options.set_capability('goog:loggingPrefs', {'performance': 'ALL'})
options.add_argument('--headless')
driver = webdriver.Chrome(options=options)

C

from selenium import webdriver
from selenium.webdriver.chrome.service import Service
from selenium.webdriver.chrome.options import Options
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities

caps = DesiredCapabilities.CHROME.copy()
caps['goog:loggingPrefs'] = {'performance': 'ALL'}

options = Options()
options.add_argument('--headless=new')

service = Service()
driver = webdriver.Chrome(service=service, options=options, desired_capabilities=caps)

D

from selenium import webdriver
from selenium.webdriver.chrome.options import Options

options = Options()
options.add_argument('--enable-logging')
driver = webdriver.Chrome(options=options)

💡 Hint

Check how to enable performance logging via DesiredCapabilities.

Option C correctly sets 'goog:loggingPrefs' in DesiredCapabilities and passes it to ChromeDriver. Option C tries to set capability on Options, which is invalid. Option C enables network via CDP but does not enable performance logs. Option C adds a logging argument but does not enable performance logs.

🧠 Conceptual

expert

What is the main limitation of capturing network logs via Selenium's performance logging?

Choose the most accurate statement about the limitations of using Selenium's performance logging to capture network traffic.

A Performance logging captures all network traffic including WebSocket frames and browser cache hits without any filtering limitations

B Performance logging disables browser caching, causing all resources to be fetched from the network every time

C Performance logging requires manual parsing of raw TCP packets, making it unsuitable for HTTP-level analysis

D Performance logging may miss some network events due to buffering and does not provide full HAR (HTTP Archive) data like dedicated proxy tools

💡 Hint

Consider what data Selenium's performance logs provide compared to specialized network tools.

Selenium's performance logging captures many network events but may miss some due to buffering and does not provide full HAR data. It does not capture raw TCP packets nor disables caching by default.

Practice

1. What is the main purpose of capturing network logs in Selenium tests?

easy

A. To see the communication between browser and server during tests

B. To speed up the test execution time

C. To change the browser's UI elements

D. To generate random test data automatically

Solution

1. Step 1: Understand network logs in Selenium

   Network logs capture the details of requests and responses between the browser and server during test execution.

2. Step 2: Identify the main purpose

   This helps testers verify if the correct URLs are called and if responses are successful.

3. Final Answer:

   To see the communication between browser and server during tests -> Option A

4. Quick Check:

   Network logs show browser-server communication [OK]

Hint: Network logs = browser-server communication details [OK]

Common Mistakes:

• Thinking network logs speed up tests
• Confusing UI changes with network logs
• Assuming network logs generate test data

2. Which Chrome option enables performance logging to capture network events in Selenium?

easy

A. "args": ["--disable-extensions"]

B. "goog:loggingPrefs": {"performance": "ALL"}

C. "prefs": {"download.default_directory": "/tmp"}

D. "chromeOptions": {"headless": true}

Solution

1. Step 1: Identify the correct Chrome option for logging

   Performance logging is enabled by setting "goog:loggingPrefs" with "performance" set to "ALL".

2. Step 2: Understand other options

   Other options like headless mode or disabling extensions do not enable network log capture.

3. Final Answer:

   "goog:loggingPrefs": {"performance": "ALL"} -> Option B

4. Quick Check:

   Enable performance logs with goog:loggingPrefs [OK]

Hint: Use goog:loggingPrefs with performance ALL to capture network logs [OK]

Common Mistakes:

• Confusing headless mode with logging
• Using download preferences for network logs
• Disabling extensions instead of enabling logs

3. Given this code snippet, what will be printed?

logs = driver.get_log('performance')
for entry in logs:
    message = json.loads(entry['message'])['message']
    if message['method'] == 'Network.responseReceived':
        print(message['params']['response']['url'])

medium

A. All browser console error messages

B. Only URLs of failed network requests

C. All URLs of network responses received during the test

D. List of all clickable elements on the page

Solution

1. Step 1: Understand the log parsing code

   The code reads performance logs, filters for 'Network.responseReceived' events, and prints the response URLs.

2. Step 2: Identify what is printed

   It prints all URLs for network responses received, regardless of success or failure.

3. Final Answer:

   All URLs of network responses received during the test -> Option C

4. Quick Check:

   Code prints URLs from Network.responseReceived events [OK]

Hint: Network.responseReceived logs contain all response URLs [OK]

Common Mistakes:

• Assuming only failed URLs are printed
• Confusing network logs with console errors
• Thinking it lists page elements

4. What is wrong with this code snippet for capturing network logs?

options = webdriver.ChromeOptions()
options.set_capability('loggingPrefs', {'performance': 'ALL'})
driver = webdriver.Chrome(options=options)
logs = driver.get_log('performance')

medium

A. The capability key should be 'goog:loggingPrefs', not 'loggingPrefs'

B. The ChromeOptions object cannot be used with Chrome driver

C. The get_log method does not exist in Selenium

D. Performance logs cannot be captured in Chrome

Solution

1. Step 1: Check capability key correctness

   The correct key to enable performance logging is 'goog:loggingPrefs', not 'loggingPrefs'.

2. Step 2: Verify other statements

   ChromeOptions can be used with Chrome driver, get_log exists, and performance logs can be captured.

3. Final Answer:

   The capability key should be 'goog:loggingPrefs', not 'loggingPrefs' -> Option A

4. Quick Check:

   Use 'goog:loggingPrefs' to enable performance logs [OK]

Hint: Use 'goog:loggingPrefs' key for performance logging [OK]

Common Mistakes:

• Using wrong capability key
• Thinking ChromeOptions is incompatible
• Believing get_log method is missing

5. How can you verify in Selenium that a specific API call to 'https://api.example.com/data' returned status code 200 using network logs?

hard

A. Use driver.execute_script to intercept network calls directly

B. Use driver.get_log('browser') and search for the URL string

C. Check page source for the URL and assume status 200 if found

D. Parse performance logs, find 'Network.responseReceived' events, check if response URL matches and status is 200

Solution

1. Step 1: Capture and parse performance logs

   Enable performance logging and get logs with driver.get_log('performance').

2. Step 2: Filter 'Network.responseReceived' events and check URL and status

   Look for events where response URL matches 'https://api.example.com/data' and verify status code is 200.

3. Final Answer:

   Parse performance logs, find 'Network.responseReceived' events, check if response URL matches and status is 200 -> Option D

4. Quick Check:

   Check responseReceived events for URL and status 200 [OK]

Hint: Filter Network.responseReceived logs by URL and status code [OK]

Common Mistakes:

• Using browser logs instead of performance logs
• Assuming URL presence means status 200
• Trying to intercept network calls with execute_script