Selenium is a robust test automation suite that is used for automating web-based applications. It supports multiple browsers, programming languages, and platforms.

Selenium comes in four forms-

1. Selenium WebDriver – Selenium WebDriver is used to automate web applications by directly calling the browser’s native methods.
2. The Selenium IDE Plugin – Selenium IDE is an open-source test automation tool that works on record and playback principles.
3. Selenium RC component – Selenium Remote Control(RC) is officially deprecated by Selenium and it used to work using javascript to automate the web applications.
4. Selenium Grid – Allows Selenium tests to run in parallel across multiple machines.
   
   

 Following are the advantages of Selenium-

• Selenium is open source and free to use without any licensing cost.
• It supports multiple languages like Java, Ruby, Python, etc.
• Selenium supports multi-browser testing.
• It has vast resources and helping community over the internet.
• Using Selenium IDE component, non-programmers can also write automation scripts.
• Using the Selenium Grid component, distributed testing can be carried out on remote machines.
  
  

 Following are the limitations of Selenium-

• We cannot test desktop applications using Selenium.
• We cannot test web services using Selenium.
• For creating robust scripts in Selenium Webdriver, programming language knowledge is required.
• Also, we have to rely on external libraries and tools for performing tasks like – logging(log4J), testing framework-(TestNG, JUnit), reading from external files(POI for excels), etc.
  
  

Some commonly used browsers supported by Selenium are-

• Google Chrome – ChromeDriver
• Firefox – FireFoxDriver
• Internet Explorer – InternetExplorerDriver
• Safari – SafariDriver
• HtmlUnit (Headless browser) – HtmlUnitDriver
• Android – Selendroid/Appium
•  IOS – ios-driver/Appium
  
  

 No  Selenium WebDriver uses the browser’s native method to automate the web applications. So, there is no support for testing web services using Selenium WebDriver.

The different locators in Selenium are-

1. Id
2. XPath
3. CSS selector
4. className
5. tagName
6. name
7. link text
8. partialLinkText
   
   

•  In order to locate web elements, we can use the Developer tool and plugins like Firebug.
  The developer tool can be launched by pressing F12 on the browser. Users can easily hover over any element and find its different HTML properties.
• Firebug is a plugin of Firefox that provides various development tools for debugging applications. From an automation perspective, Firebug is used specifically for inspecting web elements in order to find their attributes like id, class, name, etc. in different locators.

 Xpath or XML path is a query language that is used for selecting nodes from XML documents. Also, it is one of the locators supported by Selenium Webdriver.

• A relative XPath is a way of locating an element using an XML expression, starting from anywhere in the HTML document.
  
  
• In this way, there are different ways of creating robust relative XPaths that are unaffected by changes in other UI elements.
  Example – //input[@id=’username’]
  
  

In XPath, a single slash is used for creating absolute XPaths, beginning from the root node. Whereas double slash is used for creating relative XPaths.

Using contains() method we can locate an element by partially matching its attribute’s value. This is particularly helpful in scenarios where the attributes have dynamic values with a certain constant part.

xPath expression = //*[contains(@name,’user’)]

Basically, the above statement will match all the values of the name attribute containing the word ‘user’ in them.

•  Using ‘/..’ after the XPath expression of the child element, we can move to the parent of an element.
  For example, the locator //div[@id=”childId”]/.. will move to the parent of the div element with id value as ‘childId’.