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The primary objective of automation testing is to reduce the time and effort required by testers while ensuring the generation of precise and reliable test results. To achieve this, automation testers rely on specialized tools and practical knowledge of the system under test. 

In the domain of automation testing for web applications, several frameworks stand out as top choices, including Selenium Automation testing, Puppeteer, Cypress, Playwright, and more. The selection of a test automation framework hinges on various factors, such as language support, complexity, scalability, and the proficiency of the testing team in using the framework. However, it’s unsurprising that Selenium remains the go-to framework for automation testers and developers.

Challenging as it is to test web applications under various conditions thoroughly, we rely on tools to assist us in this endeavor. One such widely adopted tool by automation testers and developers is Selenium WebDriver. If you’re keen on gaining insights into the internal workings of Selenium Architecture, you’ve come to the right place.

In this article, we will provide a concise yet comprehensive overview of Selenium, covering its architecture, Selenium WebDriver, as well as its key features, advantages, and disadvantages. So, let’s dive right in!

A Brief Journey Through Selenium’s History!

Selenium’s inception dates back to 2004 when Jason Huggins, an engineer at Thoughtworks, recognized the limitations of manual testing. To tackle this challenge, he crafted a solution in the form of a program using JavaScript. Initially, it went by the name “JavaScript TestRunner.” However, as its potential expanded beyond expectations, Jason rebranded it as “Selenium Core” and made it open-source.

The evolution continued with the development of Selenium Remote Control (RC), also known as Selenium 1, by Paul Hammant, another skilled engineer at ThoughtWorks. Selenium RC aimed to address domain-specific issues encountered during web application testing.

This journey led to the creation of Selenium Grid, designed for parallel testing. Subsequently, Selenium IDE emerged, offering browser automation capabilities through a user-friendly record and playback feature reminiscent of tools like UFT/QTP.

In 2009, Simon Stewart, who was then working at Google, introduced a groundbreaking library known as WebDriver. This library was specifically designed for automating browser testing, aiming to tackle the complexities that Selenium RC presented. Its primary goal was to provide a straightforward and consistent interface by leveraging native browser automation APIs rather than relying on JavaScript injection.

In 2011, Selenium RC and Selenium WebDriver were amalgamated to create Selenium. Over the years, Selenium has undergone significant updates and improvements, culminating in the release of Selenium 3 in 2016. This version brought about bug fixes, security enhancements, and compatibility with modern web browsers.

The latest milestone in Selenium’s evolution is Selenium 4. It introduces many new features and enhancements compared to its predecessors and fully complies with W3C standards.

Understanding Selenium: An Overview

Selenium is an indispensable automation testing framework, streamlining the testing process for web applications across diverse browsers. It empowers testers and developers to craft automation test scripts in multiple programming languages, including Java, Ruby, NodeJS, Python, C#, PHP, Perl, and more.

Selenium boasts robust cross-browser testing capabilities, seamlessly supporting many popular web browsers like Google Chrome, Apple’s Safari, Mozilla Firefox, Microsoft Edge, Opera, and others. This flexibility extends to the execution of Selenium test scripts, written in various programming languages, ensuring smooth operation. 

Moreover, Selenium facilitates cross-platform testing, enabling test cases to run concurrently across multiple supported operating systems, including Windows, Linux, Mac OS, and Solaris. Thanks to its adaptability, Selenium remains one of the premier automation testing tools, allowing developers and automation testers to create agile and resilient automation test suites.

Key Components of Selenium

Selenium, far from a single-purpose tool, comprises a suite of testing tools, each offering unique capabilities that contribute to the development and design of automation frameworks. These components within the Selenium suite can be utilized independently or combined to amplify their effectiveness. The four core components of the Selenium framework are:

  • Selenium IDE
  • Selenium WebDriver
  • Selenium RC (Now considered obsolete and integrated with WebDriver)
  • Selenium Grid

Selenium IDE

Selenium IDE, an acronym for Integrated Development Environment, is a Firefox plugin and stands as one of the more straightforward frameworks within the Selenium Suite. Its primary purpose is to enable script recording and playback. Selenium IDE users often transition to Selenium RC or WebDriver to create more advanced and robust test cases.

Selenium RC

Selenium RC, also called Selenium 1, held the spotlight as the primary Selenium project for an extended period until the merger with WebDriver gave birth to Selenium 2. It predominantly relies on JavaScript for automation and supports various programming languages, including Ruby, PHP, Python, Perl, C#, Java, and JavaScript. It is worth noting that Selenium RC is now officially deprecated.

Selenium WebDriver

Selenium WebDriver is a browser automation framework that accepts commands and transmits them to the browser. It operates through browser-specific drivers, establishing direct communication with the browser to exert control. Selenium WebDriver boasts compatibility with various programming languages such as Java, C#, PHP, Python, Perl, Ruby, and JavaScript. 

Additionally, it extends its support to a range of operating systems, including Windows, Mac OS, Linux, and Solaris, along with multiple browsers like Mozilla Firefox, Internet Explorer, Google Chrome (version 12.0.712.0 and above), Safari, Opera (version 11.5 and above), Android, iOS, and HtmlUnit (version 2.9 and above).

Selenium Grid

Selenium Grid complements Selenium RC, facilitating the execution of tests on different machines and concurrently running various browsers and operating systems in parallel. This capability allows for the simultaneous execution of multiple tests across other machines, each running distinct browser and OS configurations.

Selenium Architecture 

In our exploration of Selenium Architecture thus far, we’ve covered the fundamental aspects of Selenium and its diverse components. Now, let’s embark on a detailed journey to comprehend the intricacies of Selenium WebDriver’s architecture.

As previously mentioned, Selenium WebDriver and Selenium RC were harmoniously merged into a single entity known as Selenium 2.0 or WebDriver 2.0. This amalgamation marked the beginning of a continuous evolution, leading to the release of Selenium 3.0. In Selenium 3.0, the primary mode of communication between the automation test script and the web browser was the JSON Wire protocol.

However, the landscape shifted with the arrival of Selenium 4.0, where the W3C protocol replaced the JSON Wire protocol as the preferred mode of communication.

This transformative shift eliminates the need to encode and decode test case requests in Selenium 4.0. In the upcoming sections, we will delve deeper into these protocols to gain a comprehensive understanding. 

So, let’s commence by exploring the Selenium Architecture of WebDriver in Selenium 3.0 before transitioning to the Selenium Architecture of WebDriver in Selenium 4.0.

Understanding Selenium WebDriver Architecture in Selenium 3.0

In Selenium 3.0, the communication between the user test script and the web browser primarily relies on the JSON Wire protocol. This wire protocol functions as a RESTful web service utilizing JSON over HTTP. The Selenium WebDriver architecture in Selenium 3.0 encompasses four key components:

  • Selenium Client Libraries/Language Bindings
  • JSON Wire Protocol
  • Browser Drivers
  • Real Browsers

Now, let’s dive deeper into each of the critical components of Selenium 3.0:

Selenium Client Libraries

Selenium empowers automation scripts to interact with its framework through Selenium WebDriver in various programming languages such as Ruby, Java, C#, Python, JavaScript, and more. Selenium developers have created client libraries or language bindings to facilitate this versatility. In the form of Jar files, these libraries encompass the essential methods and classes required to develop automation scripts. Installation of Selenium core libraries is straightforward, thanks to the package installers available for each supported programming language. 

Additionally, you can obtain these libraries from the official Selenium download page. It’s important to note that a Selenium client library is not a testing framework but an application programming interface (API) that enables the execution of Selenium commands from the test script.

JSON Wire Protocol

JSON (JavaScript Object Notation) is a well-known data interchange format based on a subset of the JavaScript Programming Language. Selenium WebDriver 3.0 leverages JSON to establish communication between Selenium client libraries and browser drivers. JSON’s support for data structures like arrays and objects simplifies data reading and writing. The client sends JSON requests, which are transformed into HTTP requests for the server’s comprehension. 

Upon processing, the server converts the response to JSON format before transmitting it to the client. This data transfer process, known as serialization, allows the server to interact with Selenium client libraries regardless of the underlying programming language. It effectively shields the internal workings of the browser.

Browser Drivers

Browser drivers are crucial intermediaries between Selenium client libraries and actual web browsers. They facilitate the execution of Selenium commands on browsers, including actions like mouse clicks, page navigation, and button clicks. For each supported browser in Selenium, a specific browser driver exists. These drivers receive commands from Selenium test scripts and relay them to the corresponding browsers. 

When a Selenium automation test is initiated, a sequence of actions unfolds: 

  1. Each test command generates an HTTP request using the JSON Wire Protocol, which is then dispatched to the browser driver. 
  2. The HTTP request flows through the HTTP Server, which directly manages command execution on the real browser. 
  3. The browser subsequently reports the test status to the HTTP Server, which forwards it to the automation script. 

This orchestration enables seamless communication between Selenium automation scripts and various browsers while safeguarding the browsers’ internal logic. Some notable browser drivers in Selenium include ChromeDriver, FirefoxDriver, SafariDriver, OperaBrowser, EdgeDriver, and HtmlUnitDriver.

Real Browsers

Real browsers represent the web browsers used for browsing and viewing content on the World Wide Web (WWW). This segment of the Selenium WebDriver architecture in Selenium 3.0 is straightforward: the browser receives commands and invokes the corresponding functions or methods to execute the desired automation tasks. The Selenium framework supports many popular modern browsers, including Google Chrome, Mozilla Firefox, Microsoft Edge, Apple’s Safari, and more.

Understanding Selenium WebDriver Architecture in Selenium 4.0 

Selenium 3.0’s communication medium relied on the JSON Wire protocol over HTTP. However, this approach had its limitations. It required direct communication between Selenium client libraries (such as C#, Java, Ruby, Python, etc.) and the browser driver, acting as an intermediary between the client libraries and WebDriver. 

It was necessary because the server could only comprehend protocols, not programming languages. This setup often led to slower test execution, exceptions, and increased chances of flaky tests.

Selenium WebDriver 4.0 introduced a significant W3C (World Wide Web Consortium) protocol enhancement to address these challenges. This protocol supersedes the older JSON Wire protocol, revolutionizing how Selenium communicates. 

With the introduction of the W3C protocol, there is no longer a need to encode and decode Selenium commands or API requests. Automation scripts can now directly communicate with the browser, eliminating the transfer of information via HTTP requests and responses. This improvement streamlines communication and enhances the efficiency and reliability of Selenium tests.

In Selenium 4.0, the architecture of Selenium WebDriver revolves around four major components:

  • Selenium Client Libraries/Language Bindings
  • WebDriver W3C Protocol
  • Browser Drivers
  • Real Browsers

Notably, the components in Selenium WebDriver 4.0 closely resemble those of Selenium 3.0, with one pivotal difference: replacing the JSON Wire protocol with the new W3C WebDriver protocol. Now, let’s dive into this protocol in more detail.

WebDriver W3C Protocol: A New Era in Selenium 4.0

In Selenium 4.0, the spotlight is on the ‘WebDriver W3C’ protocol, a recent addition that has garnered the endorsement of W3C, the community dedicated to web standards development. Monitoring the progress of the WebDriver W3C Protocol is made easy through the W3C Editor’s Draft and W3C Working Draft, valuable resources for staying updated on its advancements.

The essence of the WebDriver W3C Protocol lies in its direct exchange of information between the server and client, eliminating the need for the JSON Wire Protocol. This streamlined communication ensures that Selenium WebDriver and web browsers adhere to the same protocol, resulting in more consistent automated testing across different browsers.

With the WebDriver W3C Protocol in action, developers and automation testers are spared the need to make script adjustments to accommodate various web browsers. Its pivotal advantages to Selenium 4.0 include enhanced test consistency and stability, marking a significant milestone in automation testing.

What Makes Selenium 3 Different from Selenium 4?

With the release of Selenium 4, significant differences have emerged when compared to Selenium 3. Here’s a breakdown of these distinctions:

Communication Enhancement:

Selenium 3 relies on the JSON Wire protocol for client-server communication over HTTP, involving serialization and deserialization of data to JSON format. In Selenium 4, direct communication between the client and server is established, eliminating the need for the JSON Wire protocol.

W3C Compliance:

Selenium 3 does not fully conform to W3C standards, while Selenium 4 is entirely W3C compliant, aligning with W3C guidelines.

Selenium Grid Improvement:

Selenium Grid 3 required testers to start a hub and node jars separately for test automation execution. In Selenium Grid 4, these components are packaged into a single jar, streamlining the automation testing process.

ChromeDriver Update:

Selenium 3 had the ChromeDriver class directly extending RemoteWebDriver. In Selenium 4, the ChromeDriver class extends ChromiumDriver.

Selenium IDE Enhancements:

Selenium IDE in Selenium 3 only supported the Firefox browser, but Selenium 4 extends its support to Chrome. It introduces a new Plugin system that easily integrates various browsers into Selenium IDE, supporting locator strategies and IDE plugins. It also facilitates parallel test execution and offers metrics on test results.

Relative Locators:

Selenium 4 introduces Relative Locators, a feature absent in Selenium 3. These locators enable the identification of elements based on their proximity to other web elements on the page using methods such as above(), below(), toLeftOf(), toRightOf(), and near().

ChromeDevTools Protocol (CDP):

Selenium 3 lacks support for ChromeDevTools Protocol, whereas Selenium 4 embraces CDP. This integration grants access to advanced browser debugging and automation capabilities, including DOM inspection, performance profiling, and network traffic analysis.

In addition to these differences, the WebDriver W3C protocol also introduces changes in error codes, data structures, and response status codes. Further details on these changes can be found on the official Selenium Changelog page.

Benefits of Selenium WebDriver W3C Protocol in Selenium 4.0

The implementation of the WebDriver W3C protocol in Selenium 4.0 brings forth several noteworthy advantages, including the following:

  1. Enhanced Stability:

Automated Selenium testing becomes more stable and consistent across various web browsers since the browsers and Selenium WebDriver utilize the same protocol. This synchronization enhances the reliability of test runs.

  1. Improved Reliability:

The WebDriver W3C Protocol contributes to more reliable and less error-prone automated Selenium testing. Increased stability in automation testing is a compelling reason to transition to Selenium 4.0.

  1. Richer Actions API:

The new WebDriver W3C protocol leverages the Actions API, which offers more extraordinary richness than the JSON Wire Protocol. It enables the execution of multi-touch actions, zooming in and out, simultaneous pressing of multiple keys, and other advanced interactions.

  1. Advanced Gesture Support:

For instance, the W3C Protocol defines the Pinch-in sequence through an action sequence involving three ticks with two-pointer devices of type-touch. Each tick performs a series of actions, including pointerDown, pointerMove, and pointerUp, allowing for intricate multi-touch interactions.

  1. Promoting Compatibility:

Standardization through W3C opens up opportunities for broader compatibility beyond WebDriver API implementations. This standardization fosters a more consistent testing environment.

  1. Reduced Maintenance Efforts:

Web applications complying with W3C standards lead to cleaner code, resulting in improved code readability. This, in turn, reduces maintenance efforts, making test scripts more manageable and sustainable over time.

The WebDriver W3C protocol in Selenium 4.0 introduces a host of benefits that enhance the efficiency and effectiveness of automated Selenium testing.

To take your Selenium test automation to the next level, it’s worth exploring cloud-based automation testing platforms such as LambdaTest. 

LambdaTest streamlines the intricate task of cross-browser testing by granting access to a vast grid of authentic web browsers and operating systems. This allows you to execute your Selenium tests simultaneously across diverse testing environments seamlessly. LambdaTest is an AI-driven test orchestration and execution platform designed to enable the effortless execution of manual and automated tests on a large scale.

By adopting this approach, you not only boost testing efficiency but also ensure comprehensive test coverage. It is crucial for delivering flawless digital experiences to your users, regardless of their web browser or operating system choice. 

With LambdaTest, you can seamlessly integrate the Selenium WebDriver W3C Protocol into your testing workflow. This integration results in faster and more reliable testing outcomes, ultimately leading to higher-quality web applications.

Additionally, LambdaTest offers a user-friendly interface and a suite of features designed to simplify the testing process. It provides features like screenshot testing, responsive testing, and a test scheduler, enabling you to identify and rectify issues quickly. With real-time testing and debugging capabilities, LambdaTest ensures that your Selenium WebDriver W3C Protocol tests are efficient and highly effective. By harnessing the power of LambdaTest, you can easily streamline your testing efforts and achieve superior web application quality.

In Conclusion

Upon completing this comprehensive exploration of Selenium Architecture, you now possess a deeper understanding of the following key aspects:

  • Selenium WebDriver, a vital component of the Selenium suite, serves as the cornerstone of Selenium’s capabilities. Additionally, Selenium includes other components such as Selenium IDE, Selenium Grid, and the now-deprecated Selenium RC.
  • Selenium WebDriver comprises several key elements, including Selenium client libraries, JSON Wire protocol, browser drivers, and real browsers. These components work in harmony to facilitate interactions with various web browsers.
  • Selenium 3.0 primarily utilized the JSON Wire protocol over HTTP for communication between Selenium client libraries and browser drivers. In Selenium 4.0, this protocol has been replaced with the advanced WebDriver W3C protocol. 
  • Selenium proves to be a dependable and robust framework for automated web application testing. However, consider implementing cross-browser testing using a cloud-based digital experience testing platform like LambdaTest for enhanced efficiency, scalability, and faster performance.

By gaining insights into Selenium’s architecture and evolving protocols, you are better equipped to harness its capabilities for effective web application testing.

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