What is the purpose of the Selenium tool and how is it used in web application testing automation?

Selenium is a tool for automating web application testing. Its main purpose is to simulate user actions in a browser (clicks, text input, navigation, etc.) to verify the correctness of the web interface.

Application of Selenium in automation testing includes:

• Writing scripts that open a browser and perform a sequence of actions.
• Checking the display of elements, their states, and behavior during interaction.
• Regression testing to ensure new changes do not break existing functionality.
• Cross-browser testing, as Selenium supports different browsers.

Example in Python using Selenium WebDriver:

from selenium import webdriver
from selenium.webdriver.common.by import By

# Launch browser
browser = webdriver.Chrome()

# Open page
browser.get('https://example.com')

# Find element and click
button = browser.find_element(By.ID, 'submit')
button.click()

# Check result
assert 'Thank you' in browser.page_source

browser.quit()

Thus, Selenium helps automate routine checks and improve web application quality.