Docker containers for test execution in Selenium Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a Selenium WebDriver inside a Docker container.

Selenium Python

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

service = Service('[1]')
driver = webdriver.Chrome(service=service)
driver.get('https://example.com')
driver.quit()

Drag options to blanks, or click blank then click option'

A/usr/bin/chromedriver

B/usr/local/bin/geckodriver

C/bin/selenium

D/usr/bin/firefoxdriver

Attempts:

3 left

💡 Hint

Common Mistakes

Using the path for GeckoDriver instead of ChromeDriver.

Using a non-existent driver path inside the container.

The correct path for ChromeDriver in the Docker container is /usr/bin/chromedriver. This allows Selenium to control Chrome inside the container.

2fill in blank

medium

Complete the Docker command to run a Selenium test with Chrome in headless mode.

Selenium Python

docker run -d -p 4444:4444 --shm-size=2g selenium/standalone-chrome:latest [1]

Drag options to blanks, or click blank then click option'

A--headless

B--privileged

C--detach

D--rm

Attempts:

3 left

💡 Hint

Common Mistakes

Using --headless as a Docker option instead of a browser argument.

Using --privileged unnecessarily.

The --rm option removes the container after it stops, which is useful for test runs to keep the system clean.

3fill in blank

hard

Fix the error in the Selenium test code to connect to the remote WebDriver in Docker.

Selenium Python

from selenium import webdriver
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities

options = webdriver.ChromeOptions()
options.add_argument('--headless')
driver = webdriver.Remote(command_executor='http://[1]:4444/wd/hub', desired_capabilities=DesiredCapabilities.CHROME, options=options)
driver.get('https://example.com')
driver.quit()

Drag options to blanks, or click blank then click option'

A127.0.0.1

Blocalhost

Cdockerhost

D0.0.0.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0.0.0.0 which is not a valid target address.

Using dockerhost which is not a standard hostname.

When running Selenium tests locally connecting to Docker, localhost is the correct hostname to reach the Selenium server inside the container.

4fill in blank

hard

Fill both blanks to create a Docker Compose service for Selenium Chrome with proper port and shared memory size.

Selenium Python

""version: '3'
services:
  selenium-chrome:
    image: selenium/standalone-chrome:latest
    ports:
      - '[1]:4444'
    shm_size: '[2]'
"""

Drag options to blanks, or click blank then click option'

A4444

B5555

C2g

D512m

Attempts:

3 left

💡 Hint

Common Mistakes

Mapping the wrong port number.

Setting shared memory size too small causing browser crashes.

The Selenium server listens on port 4444, so mapping host port 4444 to container port 4444 is standard. The shared memory size 2g helps Chrome run smoothly inside the container.

5fill in blank

hard

Fill all three blanks to write a Python dictionary comprehension that filters test results with status 'passed' and maps test names to durations.

Selenium Python

test_durations = {test[1] test_results if test_results[test]['status'] [2] 'passed'}
result = {k: v[3] for k, v in test_durations.items()}

Drag options to blanks, or click blank then click option'

A['name']

B==

C* 1000

D[test]

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect dictionary keys.

Using assignment '=' instead of comparison '=='.

Forgetting to multiply duration to convert units.

The comprehension uses test_results[test] to access each test's data. It filters where status == 'passed'. Then it multiplies the duration by 1000 to convert seconds to milliseconds.

Practice

1. What is the main benefit of using Docker containers for Selenium test execution?

easy

A. They replace the need for writing test scripts

B. They provide a clean, consistent environment for tests to run

C. They automatically fix test failures

D. They make tests run faster on any machine

Solution

1. Step 1: Understand Docker container purpose

   Docker containers isolate the environment so tests run the same everywhere.

2. Step 2: Compare options

   Only They provide a clean, consistent environment for tests to run correctly describes this benefit; others are incorrect or unrelated.

3. Final Answer:

   They provide a clean, consistent environment for tests to run -> Option B

4. Quick Check:

   Docker containers = consistent test environment [OK]

Hint: Docker isolates environment to avoid setup issues [OK]

Common Mistakes:

• Thinking Docker speeds up tests automatically
• Believing Docker fixes test code errors
• Confusing Docker with test script writing

2. Which Python Selenium WebDriver URL should you use to connect to a Selenium server running inside a Docker container?

easy

A. "http://localhost:4444/wd/hub"

B. "http://127.0.0.1:8080"

C. "http://docker:5555"

D. "http://0.0.0.0:80"

Solution

1. Step 1: Identify default Selenium server URL in Docker

   The Selenium server in Docker usually listens on port 4444 at localhost.

2. Step 2: Match URL options

   Only "http://localhost:4444/wd/hub" matches the standard Selenium Docker URL format.

3. Final Answer:

   "http://localhost:4444/wd/hub" -> Option A

4. Quick Check:

   Default Selenium Docker URL = localhost:4444/wd/hub [OK]

Hint: Selenium Docker server default port is 4444 [OK]

Common Mistakes:

• Using wrong port numbers
• Using IPs other than localhost
• Missing the /wd/hub path

3. Given this Python code snippet connecting to a Selenium Docker container, what will be the output if the container is not running?

from selenium import webdriver
from selenium.common.exceptions import WebDriverException

try:
    driver = webdriver.Remote(
        command_executor='http://localhost:4444/wd/hub',
        options=webdriver.ChromeOptions()
    )
    print("Connected")
except WebDriverException:
    print("Connection failed")

medium

A. Connection failed

B. Connected

C. SyntaxError

D. TimeoutError

Solution

1. Step 1: Understand connection attempt

   The code tries to connect to Selenium server at localhost:4444.

2. Step 2: Consider container not running

   If the container is down, connection fails and WebDriverException is raised, triggering except block.

3. Final Answer:

   Connection failed -> Option A

4. Quick Check:

   Container down causes WebDriverException = "Connection failed" [OK]

Hint: If container off, connection throws WebDriverException [OK]

Common Mistakes:

• Expecting 'Connected' even if container is off
• Confusing exception types
• Thinking code has syntax errors

4. You wrote this Docker command to run Selenium server:

docker run -d -p 4444:4444 selenium/standalone-chrome

But your Selenium Python tests fail to connect. What is the most likely issue?

medium

A. You used the wrong port mapping in Docker command

B. You forgot to install Selenium Python package

C. Docker container is not running or crashed

D. Your test code uses an incorrect WebDriver import

Solution

1. Step 1: Check Docker container status

   If tests can't connect, first check if container is running or crashed.

2. Step 2: Evaluate other options

   The other options are less likely because the Docker command uses correct port mapping and Selenium package or imports cause different errors.

3. Final Answer:

   Docker container is not running or crashed -> Option C

4. Quick Check:

   Connection fails if container stopped = Docker container is not running or crashed [OK]

Hint: Check container running status first when connection fails [OK]

Common Mistakes:

• Assuming code import errors cause connection failure
• Ignoring container crash possibility
• Confusing port mapping syntax

5. You want to run multiple Selenium Python tests in parallel using Docker containers. Which approach best ensures isolated, reliable test runs?

hard

A. Run tests locally without Docker to avoid container overhead

B. Run all tests in a single container sharing the same browser session

C. Use Docker but share the same Selenium server URL for all tests

D. Run one Docker container per test with unique ports and clean state

Solution

1. Step 1: Understand parallel test isolation

   Running one container per test ensures each test has a clean browser and no interference.

2. Step 2: Evaluate other options

   Sharing containers or sessions risks test interference and flaky results; running locally loses Docker benefits.

3. Final Answer:

   Run one Docker container per test with unique ports and clean state -> Option D

4. Quick Check:

   Parallel tests need isolated containers = Run one Docker container per test with unique ports and clean state [OK]

Hint: Use separate containers per test for isolation [OK]

Common Mistakes:

• Sharing one container causing test conflicts
• Ignoring container cleanup between tests
• Running tests locally losing environment consistency