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Selenium Grid - Create Test Script

Selenium Grid consists of six components namely, the Router, Distributor, Nodes, Session Queue, Session Map, and Event Bus which enables the option to deploy it in various ways. Depending on the requirements, we can begin each of the components of the Selenium Grid individually in a Distributed mode, segregate them as Hub and Node in the Hub and Node mode, and all at once in a Standalone mode.

Standalone Mode in Selenium Grid

In a Standalone Mode, every component of Selenium Grid works as a single unit and can be triggered with a single command using a single process. It is the most convenient way to run the Selenium Grid. The server connects with the RemoteWebdriver requests on http://localhost:4444 and locates all the drivers from the System path automatically. Post triggering the Selenium Grid in Standalone mode, all the tests should use http://localhost:4444.

Benefits of Standalone Mode in Selenium Grid

The benefits of Standalone Mode in Selenium Grid are listed below −

  • Create and troubleshoot tests built using the RemoteWebdriver locally.

  • Executing and unit testing quickly prior to pushing the code.

  • Can be easily configured with CI/CD tools.

Hub and Node Mode in Selenium Grid

In Selenium Grid, the Hub comprises the components namely the Router, Session Map, Session Queue, and the Event Bus. The server connects with the RemoteWebdriver requests on http://localhost:4444 automatically.

The Node locates all the drivers from the System path during the starting point. Multiple Nodes can execute in the same machine. For example, if there are two Nodes, A and B running in the same machine, using the below commands −

For Node A,

java -jar selenium-server-<version>.jar node --port 5555

For Node B,

java -jar selenium-server-<version>.jar node --port 6666

The Hub and Node can be positioned on different machines where they communicate via the HTTP and the Event Bus. The Node directs messages to the Hub using the Event Bus for registration. Once the Hub gets the message, it extends to the Node using the HTTP to check its presence.

For registering a Node properly to the Hub, the Event Bus ports(default ports: 4442 and 4443) need to be available on the Hub machine and to the Nodes. This helps to establish the connection between the Hub and the Node. In case the Hub is utilizing the default ports, the --hub flag is used to register the Node as shown in the below command.

java -jar selenium-server-<version>.jar node --hub http://<hub-ip>:4444

If the Hub is not utilizing the default ports, the flags --publish-events and --subscribe-events are used as shown in the below command.

java -jar selenium-server-<version>.jar hub 
   --publish-events tcp://<hub-ip>:8886 
   --subscribe-events tcp://<hub-ip>:8887 --port 8888

In the above example, the Hub is using the ports 8886, 8887, and 8888. After the Hub is registered, the Node uses the same ports for successful registration using the same Hub ports as shown in the below command.

java -jar selenium-server-<version>.jar node 
   --publish-events tcp://<hub-ip>:8886 
   --subscribe-events tcp://<hub-ip>:8887

Benefits of Hub and Node mode in Selenium Grid

In Selenium Grid, it is observed that the Hub and Node mode is the most commonly used mode. The benefits of Hub and Node Mode in Selenium Grid are listed below −

  • The Hub and Node mode allows integration of various machines having different platforms, browsers, and their versions in the Selenium Grid.

  • The Hub and Node mode runs by pointing to one entry to execute the WebDriver tests in various environments.

  • The tests can be scaled up and down easily without impacting the complete Grid.

Distributed Mode in Selenium Grid

In a Distributed mode, each component of the Selenium Grid should be ideally positioned at different machines and they need to be kicked off separately. It is mandatory to utilize every port correctly to have correct interaction among all components.

To start with the Event Bus allows communication among Grid components. The default ports for the Event Bus are 4442, 4443, and 5557.

java -jar selenium-server-<version>.jar event-bus 
   --publish-events tcp://<event-bus-ip>:4442 --subscribe-events
   tcp://<event-bus-ip>:4443 --port 5557

Then the New Session Queue appends a new session to the queue which will be obtained by the Distributor. The default ports for the New Session Queue is 5559.

java -jar selenium-server-<version>.jar sessionqueue --port 5559

The Session Map connects the session id to the Node where the session is executing and also communicates with the Event Bus. The default port for the New Session Queue is 5556.

java -jar selenium-server-<version>.jar sessions 
   --publish-events tcp://<event-bus-ip>:4442
   --subscribe-events tcp://<event-bus-ip>:4443 --port 5556

The Distributor obtains the New Session Queue for new session requests to the Node provided their capabilities are similar. The Nodes are registered to the Distributor in the similar way a Node is registered in a Hub and Node mode. The default port for the Distributor is 5553. The Distributor communicates with the New Session Queue, Session Map, Event Bus, and the Nodes.

java -jar selenium-server-<version>.jar distributor 
   --publish-events tcp://<event-bus-ip>:4442 --subscribe-events
   tcp://<event-bus-ip>:4443 --sessions 
   http://<sessions-ip>:5556 --sessionqueue 
   http://<new-session-queue-ip>:5559 --port 5553 --bind-bus false

The Router changes the new session requests to the queue, and forwards the running session requests to the Node which is running the session. The default port for the Router is 4444. The Router communicates with the New Session Queue, Session Map, and the Distributor.

java -jar selenium-server-<version>.jar router --sessions 
   http://<sessions-ip>:5556 --distributor 
   http://<distributor-ip>:5553 --sessionqueue 
   http://<new-session-queue-ip>:5559 --port 4444

The default port for Node is 5555.

java -jar selenium-server-<version>.jar node 
   --publish-events tcp://<event-bus-ip>:4442 
   --subscribe-events tcp://<event-bus-ip>:4443

Benefits of Distributed Mode in Selenium Grid

The Distributed mode of Selenium Grid is used when there is a requirement to set up a large number of Nodes within a big size Grid(where there is only one Hub and so many Nodes across multiple machines). In such a situation, Hub and Node mode is not an ideal choice.

Prerequisites to Create a Test Script

Step 1 − Install Java(version above 8) in the system and check if it is present with the command: java -version. The java version installed will be visible if installation has been completed successfully.

Step 2 − Check Grid status by opening a browser and entering −

  • For the UI version, type http://localhost:4444.

  • For Non UI version, type http://localhost:4444/status.

For both the cases, we would get the error - This site can’t be reached. Since Selenium Grid has not been started yet.

Selenium Grid Create Test Script 1

Create a Test Script in Selenium Grid

The steps to create a test script in a Standalone mode are listed below −

Step 1 − Download Selenium Standalone Jar from the below link and save it in a folder −

https://github.com/SeleniumHQ/selenium/releases.

Step 2 − From the location of the folder where the Selenium Standalone Jar had been stored, run the below command from the terminal −

java -jar selenium-server-<version>.jar standalone.

Step 3 − Check Grid status again by opening a browser and entering: http://localhost:4444.

The Error − This site can’t be reached would no longer be there, and we would get Grid status showing different browsers. This would prove Selenium Grid had been triggered in the Standalone mode.

Selenium Grid Create Test Script 2

Step 4 −

Code Implementation in Base.java

package BaseClass;

import java.net.MalformedURLException;
import java.net.URL;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.remote.DesiredCapabilities;
import org.openqa.selenium.remote.RemoteWebDriver;

public class Base {
   public WebDriver setBrowser(String browserName) throws MalformedURLException {
      WebDriver driver = null;
      DesiredCapabilities dc = new DesiredCapabilities();

      if(browserName.equalsIgnoreCase("chrome")) {
         dc.setBrowserName("chrome");
      } else if(browserName.equalsIgnoreCase("edge")) {
         dc.setBrowserName("MicrosoftEdge");
      }

      // Initiate RemoteWebDriver
      driver = new RemoteWebDriver(new URL("http://localhost:4444"),dc);
      return driver;
   }
}

Code Implementation in TestOne.java

package Grid;

import BaseClass.Base;
import org.openqa.selenium.WebDriver;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.Test;
import java.net.MalformedURLException;

public class TestOne extends Base {
   public WebDriver driver = null;
   @Test
   public void testOne() {
   
      // launch application
      driver.get("https://www.tutorialspoint.com/selenium/practice/links.php");

      // get page title
      System.out.println("Page title is: " + driver.getTitle() + " obtained from testOne");
   }

   @BeforeMethod
   public void setup() throws MalformedURLException {
      driver = setBrowser("chrome");
   }

   @AfterMethod
   public void tearDown() {
   
      // quitting browser
      driver.quit();
   }
}

Code Implementation in TestTwo.java

package Grid;

import BaseClass.Base;
import org.openqa.selenium.WebDriver;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.Test;
import java.net.MalformedURLException;

public class TestTwo extends Base {
   public WebDriver driver = null;
   @Test
   public void testTwo() {
   
      // launch application
      driver.get("https://www.tutorialspoint.com/selenium/practice/links.php");

      // get page title
      System.out.println("Page title is: " + driver.getTitle() + " obtained from testTwo");
   }
   @BeforeMethod
   public void setup() throws MalformedURLException {
      driver = setBrowser("edge");
   }
   @AfterMethod
   public void tearDown() {
   
      // quitting browser
      driver.quit();
   }
}

Configurations in testng.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd">
<suite name = "Grid Test">
   <test thread-count = "5" name="Test">
      <classes>
         <class name="Grid.TestOne" />
         <class name="Grid.TestTwo"/>
      </classes>
   </test>
</suite>

Step 5 − Run the test from the testng.xml file.

It will show the following output −

Page title is: Selenium Practice - Links obtained from testOne
Page title is: Selenium Practice - Links obtained from testTwo

===============================================
Grid Test
Total tests run: 2, Passes: 2, Failures: 0, Skips: 0
===============================================

Process finished with exit code 0

In the above example, we had configured the Standalone mode of the Selenium Grid.

This concludes our comprehensive take on the tutorial on Selenium Grid - Create Test Script. We’ve started with describing Standalone, Hub and Node, and Distributed modes in Selenium Grid and their benefits, prerequisites to create a test script, and how to create a test script in Selenium Grid.

This equips you with in-depth knowledge of the Selenium Grid - Create Test Script. It is wise to keep practicing what you’ve learned and exploring others relevant to Selenium to deepen your understanding and expand your horizons.

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