Selenium IDE is a Chrome and Firefox plugin. The primary use of a Selenium IDE is to record user interactions such as clicks, selections etc in the browser and plays them back as automated tests . 

It then generates the test script (of the automated tests) in programming languages like C#, Java, Python, and Ruby and Selenese (Selenium’s own scripting language).

Selenium IDE helps in:

• Creating automated test scripts and validating them at speed
• Identifying and highlighting errors during the replay of interactions
• Cross Browser Testing

Useful Resources to learn about Selenium IDE

• Getting Started with Selenium IDE
• Features of Selenium IDE 
• How to Effectively Use Record and Playback
• Selenium IDE Alternatives

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Selenium RC was built to automate the testing of web applications by simulating user interactions across different browsers and platforms. It provided a way to browser automation remotely and execute test scripts written in various programming languages.

Limitations of Selenium RC:

• Browser Limitations: Selenium RC had to work with browsers using a JavaScript-based “proxy” mechanism, which introduced potential instability and limitations, especially when working with modern web applications.
• Speed and Performance: The use of a JavaScript proxy added overhead and affected the speed and performance of test execution.
• Maintenance and Compatibility: Selenium RC required separate “drivers” for each browser, making maintenance and compatibility challenging as browsers continued to update and evolve.
• Synchronization Issues: Selenium RC often faced synchronization problems, where test scripts had to wait for the browser to respond before proceeding to the next step.
• Complex Setup: Setting up Selenium RC involved multiple components, which could be complex and difficult to configure correctly.

Selenium WebDriver is a powerful and enhanced version of Selenium RC which was developed to overcome the limitations of Selenium RC. WebDriver communicates with browsers directly with the help of browser-specific native methods, thereby completely eliminating the need of Selenium RC.

WebDriver works closely with Selenium IDE and Selenium Grid resulting in reliable test execution at speed and scale.

Selenium Grid is a smart proxy server that allows QAs to run tests in parallel on multiple machines. This is done by routing commands to remote web browser instances, where one server acts as the hub. This hub routes test commands that are in JSON format to multiple registered Grid nodes.

Selenium WebDriver is an open source tool to perform Browser Automation on real browsers. WebDriver communicates with browsers directly using client libraries and JSON wire protocol. It helps testers ensure that the website functions as intended on different browsers.

Selenium WebDriver is primarily designed to test web applications. You can perform:

• Functional Testing: Test the functionality of web applications by automating user interactions such as clicking buttons, filling out forms, navigating pages, and verifying expected outcomes.
• Cross-Browser Testing: Test web application for consistency across different browsers and browser versions (e.g., Chrome, Firefox, Edge, Safari) 

Read More: Cross Browser Testing in Selenium : Tutorial

• Cross-Platform Testing: Test the web application on different operating systems sucn as Windows, macOS, and Linux. 
• Regression Testing: Test the existing functionality of the web app, whenever a new feature is introduced.

Read More: Regression Testing with Selenium: Tutorial

• Data-Driven Testing: Execute the same test script with different sets of input data to validate different scenarios.
• Parallel Testing: Selenium WebDriver can be integrated with tools like Selenium Grid to execute tests in parallel across multiple browsers and platforms, reducing testing time.

Read More: Parallel Testing with Selenium

• Complex User Flows: Simulate complex user workflows or interactions that need to be tested repeatedly.
• Integration with Continuous Integration (CI) Pipelines: Selenium WebDriver can be seamlessly integrated into your CI/CD pipeline, enabling automated testing with every code change and ensuring code quality.
• UI/UX Testing: Automate user interface (UI) testing, ensuring that the visual elements and layout of your application are consistent.

Also Read: How to perform UI Testing with Selenium

• End-to-End Testing: Selenium WebDriver can be used for end-to-end testing, where you simulate real user interactions across different parts of the application to ensure a seamless user experience.
• Page Object Model (POM) Implementation: If you adopt the Page Object Model (POM) design pattern, WebDriver can be used effectively to encapsulate the interactions and elements of different web pages, leading to more maintainable and modular test scripts.

Read More: Design Patterns in Selenium

• Complex Scenarios: When dealing with complex scenarios such as handling alerts, pop-ups, iframes, and dynamic content, Selenium WebDriver provides the flexibility to address these challenges.
• Performance Testing: While not its primary use, WebDriver can be used to simulate user load and interactions for basic performance testing.

WebDriver Architecture is made up of four major components:

• Selenium Client library: Selenium provides support to multiple libraries such as Ruby, Python, Java, etc as language bindings
• JSON wire protocol over HTTP: JSON is an acronym for JavaScript Object Notation. It is an open standard that provides a transport mechanism for transferring data between client and server on the web.
• Browser Drivers: Selenium browser drivers are native to each browser, interacting with the browser by establishing a secure connection. Selenium supports different browser drivers such as ChromeDriver, GeckoDriver, Microsoft Edge WebDriver, SafariDriver, and InternetExplorerDriver.
• Browsers: Selenium provides support for multiple browsers like Chrome, Firefox, Safari, Internet Explorer etc.

JSON wire protocol helps Selenium Language Bindings communicate with the Browser Drivers and thus automate interactions on real browsers.

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Selenium supports these Browsers:

• Google Chrome
• Mozilla Firefox
• Safari
• Internet Explorer
• Microsoft Edge

Note: Selenium 4 has terminated native support to Opera and PhantomJS browsers

The architecture of Selenium 4 is similar to Selenium 3, however it uses W3C protocol instead of JSON wire protocol for communication between Client Libraries and Browser Drivers.

W3C protocol was introduced because all the web browsers followed the W3C standards and also all the browser drivers followed the W3C standards. To standardise the communication, JSON wire protocol was replaced by W3C in Selenium 4. 

This helped in better communication with the browsers, stability, and common code (i.e. no browser specific code required). Due to W3C there is a direct transfer of information between client and server.

• Terminated native support to Opera and PhantomJS browsers
• Selenium 4 introduced relative locators (enable you to locate web elements on a page based on their relationship to other elements)
• Deprecated Desired Capabilities and replaced it with Options class
• Added new methods to Action class

Useful Resources to learn about Selenium 4:

• Selenium 4: Understanding Key Features
• Selenium 3 vs Selenium 4: Core Differences
• How to upgrade from Selenium 3 to Selenium 4

Selenium Grid is a component of the Selenium testing framework that allows you to run test scripts across multiple browsers, operating systems, and machines in parallel. It enables you to perform large-scale test automation and significantly reduces the time required for testing by executing tests simultaneously on different environments.

• Parallel testing: You can run multiple tests simultaneously on different nodes. This significantly reduces the overall test execution time and helps test at scale.
• Cross-Browser Testing: Selenium Grid is particularly useful for cross-browser testing, where you need to ensure that your web application functions correctly across different web browsers (such as Chrome, Firefox, Edge, Safari). It allows you to run your tests simultaneously on multiple browser-platform combinations.
• Cross-Platform Testing: If your web application needs to work seamlessly on different operating systems (Windows, macOS, Linux), Selenium Grid enables you to execute tests on various platforms concurrently.
• Continuous Integration (CI) Pipelines: Selenium Grid can be integrated into your CI/CD pipeline. It enables automated testing of each code change across multiple environments. This helps ensure that your application remains functional as new code is introduced.

The two major components of the Selenium Grid 3 architecture are:

• Hub is a server that accepts access requests from the WebDriver client, routing the JSON test commands to the remote drives on nodes. It takes instructions from the client and executes them remotely on the various nodes in parallel
• Node is a remote device that consists of a native OS and a remote WebDriver. It receives requests from the hub in the form of JSON test commands and executes them using WebDriver

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Unlike its predecessor, Selenium Grid 4 does not have Hub and the architecture is more sophisticated to accommodate better scalability. It consists of:

• Router:
  • It is the entry point for the client requests.Router passes new session request to Session Queue.
  • For a request of an existing session, router passes it to the Session Map which eventually is designated to a Node by assigning a NodeID.
  • The primary function of Router is to manage the load of the Grid.
• Distributor:
  • It registers and track the capabilities of all the nodes through the GridModel.
  • It queries the Session Queue and assigns the new session request to the suitable Node.
  • Once the session is created at a Node, Distributor shares the SessionID and NodeID relation in the Session Map.
• Session Map:
  • It stores the relation between a SessionID and the Node where the session is running. 
  • It helps Router in allocating the Request of a session to Node based on the SessionID.
• Session Queue:
  • It holds information about new session requests in FIFO order. 
  • This is used by Distributor and Router to assign Nodes for the Requests.
• Event Bus: It is a communication path between the Nodes, Distributor, Session Queue, and Session Map.
• Nodes: It executes the request commands on different browser drivers.

A Selenium Cloud is basically a Selenium Grid configured on cloud servers. The Cloud Selenium Grid connects to a range of browsers and real devices with different operating systems which are configured and made available 24×7 on-demand. This makes it possible for QA teams to automate tests by executing several test scripts simultaneously on multiple device-browser combinations on the cloud using parallel testing.

A Selenium cloud eliminates the overhead of maintaining and updating the physical infrastructure at regular intervals. That means organizations do not have to purchase, maintain, update devices, browsers and operating systems on-site. While maintaining physical devices require a lot of time and effort, buying subscription of a cloud based grid like BrowserStack can be a more feasible solution. 

It would allow you to conduct comprehensive testing with the latest and legacy browser versions and devices. 

Read More: Build vs Buy: How to decide between in-house lab or cloud solution

Testers can test web-applications directly on real devices on a robust and highly available cloud. BrowserStack’s real device cloud gives you access to 3000+ real devices and browsers, so that you can test you web application completely under real user conditions. QAs just need to be ready with their test scripts and device coverage requirements. Log in, select devices, start testing.

Try Selenium Cloud Testing for Free

• Programming Language and Environment: 
  • Choose a programming language for writing your Selenium test scripts. Popular choices include like Ruby, Java, PHP, Python, JavaScript, and C#.
  • Install the programming language’s development environment and necessary tools.
• Download and Install IDE: Popular Integrated Development Environment (IDE) used for for writing and managing Selenium test scripts are Eclipse, Intellij, and Visual Studio.
  Useful Resources to learn about setting up IDE for Selenium:
  • How to configure Selenium in Eclipse
  • How to set up Selenium on Visual Studio
• Download and Install Selenium WebDriver: Download and set up Selenium WebDriver for your chosen programming language. 
• Download and Configure Browser Driver: Download required browser drivers. Browser Driver Browser Drivers Supported by Selenium are:
  • ChromeDriver for Chrome and Chromium Browsers
  • GeckoDriver for Firefox Browser
  • EdgeDriver for Edge
  • SafariDriver for Safari (in-built)
• Download and Install Web Browser: Install the web browsers versions of Chrome, Firefox, Edge that are compatible with the corresponding browser drivers.
• Configure Dependencies and Libraries: Install any necessary libraries or packages such as testing frameworks (e.g., JUnit, TestNG, NUnit) or additional utility libraries.
  Useful Resources
  • JUnit Testing Tutorial: JUnit in Java
  • How to write JUnit test cases
  • Getting started with Selenium and NUnit Framework: Tutorial
  • How to Automate TestNG in Selenium

• Build and Dependency Management Tools (Optional but recommended): 
  • Use build tools like Maven, Gradle, or npm to manage project dependencies and build configurations. 
  • These tools help automate the process of downloading libraries and setting up your project.

Read More: Maven Dependency Management with Selenium

Selenium allows you to run automated tests in different programming languages. Based on the language of test script (i.e. Selenium Client Language bindings) such as Java, Python, the pre-requisites, configuration, and execution varies. Which is why it is important to follow the steps for the chosen language binding to run Selenium Automation Test in it.

Here are resources that can help you learn how to run Selenium Automation Tests in different programming languages.

• Selenium with Java
• Selenium with Python
• Selenium with JavaScript
• Selenium with PHP
• Selenium with Ruby
• Selenium with C#