Learn Selenium: Ultimate Guide to Automation Testing with Python

Selenium is a popular open-source framework for automating web browsers, often used for web testing. Here’s a structured guide to learning Selenium basics that will help you prepare for interviews:

1. Introduction to Selenium

• What is Selenium? Selenium automates browsers, enabling you to perform tasks like form submissions, navigation, clicks, and more, which are often used in testing web applications.
• Why use Selenium? It supports multiple programming languages (Java, Python, C#, etc.) and browsers (Chrome, Firefox, Safari).

2. Selenium Components

• Selenium WebDriver: Automates browser actions like clicking buttons or navigating pages.
• Selenium IDE: A record-and-playback tool, primarily used for basic test recording.
• Selenium Grid: Allows parallel test execution on different machines or browsers.
• Selenium RC (Remote Control): Older version, largely replaced by WebDriver.

3. Setup

• Install WebDriver for your browser (ChromeDriver, GeckoDriver for Firefox).
• Install Selenium Library for the language you are using (e.g., Python: pip install selenium, Java: add Selenium JAR to your project).

4. Basic Commands

Launching a browser:

from selenium import webdriver 
driver = webdriver.Chrome() # or Firefox, Safari, etc.
driver.get('http://google.com') # open the URL

Locating elements: Selenium provides several ways to locate web elements:

• find_element_by_id()

• find_element_by_name()

• find_element_by_xpath()

• find_element_by_css_selector()

element = driver.find_element_by_id('element_id')

• Clicking an element:

button = driver.find_element_by_name('submit')
button.click()

• Typing into an input field:

input_field = driver.find_element_by_name('username')
input_field.send_keys('testuser')

• Submitting a form:

form = driver.find_element_by_id('login-form')
form.submit()

• Navigating between pages:

driver.back()  # Go back
driver.forward()  # Go forward

5. Handling Web Elements

• Dropdowns:

from selenium.webdriver.support.ui import Select
select = Select(driver.find_element_by_name('dropdown'))
select.select_by_value('value1')

• Checkboxes & Radio Buttons:

checkbox = driver.find_element_by_id('agree')
checkbox.click()

• Handling Alerts:

alert = driver.switch_to.alert
alert.accept()  # Accept the alert

6. Handling Waits

Selenium supports two types of waits:

• Implicit Wait: Global wait until elements are available.

driver.implicitly_wait(10)  # Wait for 10 seconds

• Explicit Wait: Wait until a condition is met for specific elements.

from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

WebDriverWait(driver, 10).until(
    EC.presence_of_element_located((By.ID, 'element_id'))
)

7. Page Navigation and Windows

• Handling multiple windows:

driver.switch_to.window(driver.window_handles[1])  # Switch to new tab/window

• Switching to an iframe:

driver.switch_to.frame('frame_name')
driver.switch_to.default_content()  # Switch back to main content

8. Advanced WebDriver Features

Handling Multiple Windows

Selenium can interact with multiple windows or tabs opened by a browser.

# Get current window handle
main_window = driver.current_window_handle

# Open a new window and switch to it
driver.execute_script("window.open('http://example.com', '_blank');")
windows = driver.window_handles
driver.switch_to.window(windows[1])  # Switch to new window

# Switch back to the main window
driver.switch_to.window(main_window)

Switching Between Frames (iframes)

Switching between iframes is crucial when dealing with pages that have embedded content (like ads or other documents).

# Switch to iframe
driver.switch_to.frame('iframe_name')

# Perform actions inside iframe
element = driver.find_element_by_id('element_inside_iframe')

# Switch back to the main content
driver.switch_to.default_content()

9. Advanced Locators

Using Dynamic XPath and CSS Selectors

Dynamic XPath can handle complex DOM structures and elements that don’t have static attributes.

# XPath example with text content
driver.find_element_by_xpath("//button[text()='Submit']")

# XPath with contains() to handle partial matches
driver.find_element_by_xpath("//a[contains(@href, 'part_of_link')]")

# CSS Selector with dynamic attribute matching
driver.find_element_by_css_selector("input[name*='partial_name']")

10. JavaScript Execution

Selenium WebDriver can execute JavaScript in the context of the web page for scenarios where normal WebDriver actions are insufficient.

# Execute JavaScript
driver.execute_script("document.getElementById('submit').click();")

# Scroll the page using JavaScript
driver.execute_script("window.scrollTo(0, document.body.scrollHeight);")

11. Page Object Model (POM)

The Page Object Model is a design pattern that enhances the structure of test automation by separating test logic from UI interaction.

• Test Class: Contains test methods, calling methods from the page object.
• Page Object: A class representing a web page, encapsulating the web elements and actions for that page.

Example of Page Object:

class LoginPage:
    def __init__(self, driver):
        self.driver = driver

    def enter_username(self, username):
        self.driver.find_element_by_id('username').send_keys(username)

    def enter_password(self, password):
        self.driver.find_element_by_id('password').send_keys(password)

    def click_login(self):
        self.driver.find_element_by_id('login_button').click()

Test Case:

def test_login():
    driver = webdriver.Chrome()
    driver.get('http://example.com/login')
    
    login_page = LoginPage(driver)
    login_page.enter_username('testuser')
    login_page.enter_password('password123')
    login_page.click_login()
    
    # Add assertions to validate login
    assert "Dashboard" in driver.title

12. Handling File Uploads and Downloads

driver.find_element_by_id('file-upload').send_keys('C:/path_to_file/file.txt')

File Download:

options = webdriver.ChromeOptions()
prefs = {'download.default_directory': 'C:/Downloads'}
options.add_experimental_option('prefs', prefs)
driver = webdriver.Chrome(options=options)

Basic Interview Topics

• Advantages of Selenium: Open-source, supports multiple languages and browsers, cross-browser testing, etc.
• Limitations: No built-in reporting, can’t handle desktop applications.
• Locators: Understand all locators—id, name, xpath, cssSelector.
• Wait Mechanisms: Difference between implicit and explicit waits.
• Page Object Model (POM): Popular design pattern for organizing test scripts in a structured way.
• TestNG (Java): Often used in Selenium for testing, includes features like annotations and parallel testing.

Practice Tasks

• Automate a login process on a demo site.
• Practice locating elements using different locators (ID, Xpath, CSS Selector).
• Write a script that waits for a certain element to appear before interacting with it.