Desired Capabilities

Desired Capabilities are key-value pairs configuring browser or mobile device settings for automated tests. They specify the testing environment, like browser type, version, OS, and device specifics, ensuring tests run as intended.

Detailed explanation

Desired Capabilities act as a blueprint for setting up the remote WebDriver environment. They tell the WebDriver server (e.g., Selenium Grid, cloud testing platforms) exactly how to configure the browser or mobile device before a test session begins. This configuration includes specifying the browser type (Chrome, Firefox, Safari, Edge), browser version, operating system, device name (for mobile testing), screen resolution, and other environment-specific settings. Without properly defined desired capabilities, tests might fail to run correctly or produce inconsistent results due to environmental discrepancies.

The primary purpose of using desired capabilities is to achieve consistent and reliable test execution across different environments. By explicitly defining the environment in which the tests should run, we can minimize the risk of environment-related failures and ensure that the tests are accurately reflecting the application's behavior.

Practical Implementation

Desired capabilities are typically defined as a dictionary or a JSON object within the test script. The specific keys and values that are supported depend on the WebDriver implementation and the browser or device being tested.

Here's an example of how to define desired capabilities in Python using Selenium:

from selenium import webdriver
from selenium.webdriver.chrome.options import Options
 
chrome_options = Options()
chrome_options.add_argument("--headless") # Run Chrome in headless mode
 
desired_capabilities = {
    'browserName': 'chrome',
    'version': 'latest',
    'platformName': 'Windows',
    'goog:chromeOptions': chrome_options.to_capabilities()
}
 
driver = webdriver.Remote(command_executor='http://localhost:4444/wd/hub',
                          desired_capabilities=desired_capabilities)
 
driver.get("https://www.example.com")
print(driver.title)
driver.quit()

In this example, we're specifying that we want to run our tests on the Chrome browser, on the Windows platform, and using the latest available version of Chrome. We are also setting Chrome to run in headless mode, which is useful for running tests in environments where a graphical user interface is not available.

For mobile testing, the desired capabilities will be different. Here's an example using Appium:

from appium import webdriver
 
desired_caps = {
    'platformName': 'Android',
    'platformVersion': '9.0',
    'deviceName': 'emulator-5554',
    'appPackage': 'com.example.android.myApp',
    'appActivity': 'com.example.android.myApp.MainActivity'
}
 
driver = webdriver.Remote('http://localhost:4723/wd/hub', desired_caps)
 
# Perform actions on the mobile app
driver.quit()

Here, we're specifying the platform name (Android), platform version (9.0), device name (emulator-5554), and the app package and activity to launch. These capabilities are specific to mobile testing and allow Appium to correctly identify and interact with the mobile application.

Best Practices

  • Be Specific: Define the desired capabilities as precisely as possible. Avoid using generic values like "latest" unless absolutely necessary. Specifying exact versions can help prevent unexpected behavior due to browser or driver updates.
  • Use Environment Variables: Store sensitive information, such as access keys or device IDs, in environment variables instead of hardcoding them in the test scripts. This improves security and makes it easier to manage different environments.
  • Leverage Cloud Testing Platforms: Cloud testing platforms like Sauce Labs, BrowserStack, and LambdaTest provide a wide range of pre-configured environments and devices. Using these platforms can simplify the process of setting up and managing desired capabilities.
  • Capability Matching: Understand how WebDriver servers match desired capabilities with available environments. If a perfect match is not found, the server may attempt to find the closest matching environment, which could lead to unexpected results.
  • Review Documentation: Always refer to the official documentation for the specific WebDriver implementation and browser or device being tested. The supported capabilities and their values may vary.
  • Consider Headless Mode: For browser testing, consider using headless mode whenever possible. Headless mode allows you to run tests without a graphical user interface, which can improve performance and reduce resource consumption.
  • Logging: Log the desired capabilities used for each test run. This can be helpful for debugging and troubleshooting issues.

Common Tools and Frameworks

  • Selenium: A widely used framework for automating web browsers. Selenium supports defining desired capabilities through its webdriver.Remote class.
  • Appium: An open-source tool for automating native, mobile web, and hybrid applications. Appium uses desired capabilities to configure the mobile device or emulator.
  • WebDriverManager: A tool that automates the management of WebDriver binaries. It can automatically download and configure the correct WebDriver version based on the desired browser version.
  • Cloud Testing Platforms (Sauce Labs, BrowserStack, LambdaTest): These platforms provide a cloud-based infrastructure for running automated tests on a wide range of browsers and devices. They typically offer APIs or configuration options for specifying desired capabilities.

Example with WebDriverManager

from selenium import webdriver
from selenium.webdriver.chrome.service import Service
from webdriver_manager.chrome import ChromeDriverManager
 
service = Service(ChromeDriverManager().install())
driver = webdriver.Chrome(service=service)
 
driver.get("https://www.example.com")
print(driver.title)
driver.quit()

While WebDriverManager simplifies driver setup, you can still combine it with desired capabilities for more control:

from selenium import webdriver
from selenium.webdriver.chrome.service import Service
from webdriver_manager.chrome import ChromeDriverManager
from selenium.webdriver.chrome.options import Options
 
chrome_options = Options()
chrome_options.add_argument("--headless")
 
service = Service(ChromeDriverManager().install())
driver = webdriver.Chrome(service=service, options=chrome_options)
 
driver.get("https://www.example.com")
print(driver.title)
driver.quit()

In summary, desired capabilities are a crucial aspect of automated testing. By carefully defining the environment in which the tests should run, we can ensure consistent and reliable results, reduce the risk of environment-related failures, and improve the overall quality of our software. Understanding how to implement and manage desired capabilities is an essential skill for any software developer or QA engineer involved in automated testing.

Further reading

Related Terms

A/B Testing

Acceptance Testing

Accessibility Tester