Why Grid enables parallel execution in Selenium Python - Test Execution Impact

Test Overview

This test demonstrates how Selenium Grid allows running multiple tests at the same time on different browsers or machines. It verifies that tests can start and finish independently without waiting for each other.

Test Code - Selenium

Selenium Python

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.remote.webdriver import WebDriver
import threading
import time

def run_test(node_url: str, browser_name: str):
    options = webdriver.ChromeOptions() if browser_name == 'chrome' else webdriver.FirefoxOptions()
    driver: WebDriver = webdriver.Remote(
        command_executor=node_url,
        options=options
    )
    driver.get('https://example.com')
    heading = driver.find_element(By.TAG_NAME, 'h1').text
    assert heading == 'Example Domain', f'Heading mismatch on {browser_name}'
    time.sleep(2)  # Simulate test steps
    driver.quit()

if __name__ == '__main__':
    node1 = 'http://localhost:4444/wd/hub'
    node2 = 'http://localhost:4445/wd/hub'
    thread1 = threading.Thread(target=run_test, args=(node1, 'chrome'))
    thread2 = threading.Thread(target=run_test, args=(node2, 'firefox'))
    thread1.start()
    thread2.start()
    thread1.join()
    thread2.join()

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts and two threads are created for parallel execution	No browsers open yet, threads ready to run tests on different nodes	-	PASS
2	Thread 1 opens Chrome browser via Selenium Grid node at http://localhost:4444/wd/hub	Chrome browser window opens on node1, navigates to https://example.com	-	PASS
3	Thread 2 opens Firefox browser via Selenium Grid node at http://localhost:4445/wd/hub	Firefox browser window opens on node2, navigates to https://example.com	-	PASS
4	Thread 1 finds the heading element and asserts its text is 'Example Domain'	Chrome browser shows page with heading 'Example Domain'	Heading text equals 'Example Domain'	PASS
5	Thread 2 finds the heading element and asserts its text is 'Example Domain'	Firefox browser shows page with heading 'Example Domain'	Heading text equals 'Example Domain'	PASS
6	Both threads wait 2 seconds simulating test steps independently	Both browsers remain open and active on their respective nodes	-	PASS
7	Both threads close their browsers and end	No browsers open, threads complete execution	-	PASS

Failure Scenario

Failing Condition: One node URL is incorrect or node is down, causing browser not to open

Execution Trace Quiz - 3 Questions

What allows the two tests to run at the same time in this example?

A Using Selenium Grid with multiple nodes

B Running tests sequentially in one thread

C Using only one browser instance

D Running tests on the same node one after another

Key Result

Using Selenium Grid with multiple nodes enables running tests in parallel on different browsers or machines, which saves time and improves test efficiency.