Getting Started with Selenium Grid

Important preliminary points

For this section you will need to have Apache Ant on the machine that you are going to have running Grid instances. You can get this from http://ant.apache.org/bindownload.cgi for Windows and Mac. If you have Ubuntu you can simply do sudo apt-get install ant1.8, which will install all the relevant items that are needed onto your Linux machine. Visit the project site to download Selenium Grid.

Understanding Selenium Grid

Selenium Grid is a version of Selenium that allows teams to set up a number of Selenium instances and then have one central point to send your Selenium commands to. This differs from what we saw in Selenium Remote Control (RC) where we always had to explicitly say where the Selenium RC is as well as know what browsers that Remote Control can handle.

With Selenium Grid, we just ask for a specific browser, and then the hub that is part of Selenium Grid will route all the Selenium commands through to the Remote Control you want.

Selenium Grid also allows us to, with the help of the configuration file, assign friendly names to the Selenium RC instances so that when the tests want to run against Firefox on Linux, the hub will find a free instance and then route all the Selenium Commands from your test through to the instance that is registered with that environment. We can see an example of this in the next diagram.

We will see how to create tests for this later in the chapter, but for now let’s have a look at making sure we have all the necessary items ready for the grid.

Checking that we have the necessary items for Selenium Grid

Now that you have downloaded Selenium Grid and Ant, it is always good to run a sanity check on Selenium Grid to make sure that we are ready to go. To do this we run a simple command in a console or Command Prompt.

Let’s see this in action.

Time for action – doing a sanity check on Selenium Grid

1. 1. Open a Command Prompt or console window.
   2. Run the command ant sanity-check. When it is complete you should see something similar to the next screenshot:

What just happened?

We have just checked whether we have all the necessary items to run Selenium Grid. If there was something that Selenium relied on, the sanity check script would output what was needed so that you could easily correct this. Now that everything is ready, let us start setting up the Grid.

Selenium Grid Hub

Selenium Grid works by having a central point that tests can connect to, and commands are then pushed to the Selenium Remote Control instances connected to that hub. The hub has a web interface that tells you about the Selenium Remote Control instances that are connected to the Hub, and whether they are currently in use.

Time for action – launching the hub

Now that we are ready to start working with Selenium Grid we need to set up the Grid. This is a simple command that we run in the console or Command Prompt.

1. Open a Command Prompt or console window.
2. Run the command ant launch-hub. When that happens you should see something similar to the following screenshot:

   

We can see that this is running in the command prompt or console. We can also see the hub running from within a browser.

If we put http://nameofmachine:4444/console where nameofmachine is the name of the machine with the hub. If it is on your machine then you can place http://localhost:4444/console. We can see that in the next screenshot:

What just happened?

We have successfully started Selenium Grid Hub. This is the central point of our tests and Selenium Grid instances. We saw that when we start Selenium Grid it showed us what items were available according to the configuration file that is with the normal install.

We then had a look at how we can see what the Grid is doing by having a look at the hub in a browser. We did this by putting the URL http://nameofmachine:4444/console where nameofmachine is the name of the machine that we would like to access with the hub. It shows what configured environments the hub can handle, what grid instances are available and which instances are currently active.

Now that we have the hub ready we can have a look at starting up instances.

Adding instances to the hub

Now that we have successfully started the Selenium Grid Hub, we will need to have a look at how we can start adding Selenium Remote Controls to the hub so that it starts forming the grid of computers that we are expecting. As with everything in Selenium Grid, we need Ant to start the instances that connect. In the next few Time for action sections we will see the different arguments needed to start instances to join the grid.

Time for action – adding a remote control with the defaults

In this section we are going to launch Selenium Remote Control and get it to register with the hub. We are going to assume that the browser you would like it to register for is Firefox, and the hub is on the same machine as the Remote Control. We will pass in only one required argument, which is the port that we wish it to run on. However, when starting instances, we will always need to pass in the port since Selenium cannot work out if there are any free ports on the host machine.

1. 1. Open a Command Prompt or console window.
   2. Enter the command ant –Dport=5555 launch-remote-control and press Return. You should see the following in your Command Prompt or console:

      

   3. And this in the Selenium Grid Hub site:

What just happened?

We have added the first machine to our own Selenium Grid. It has used all the defaults that are in the Ant build script and it has created a Selenium Remote Control that will take any Firefox requests, located on the same machine as the host of Selenium Remote Control Grid. This is a useful way to set up the grid if you just want a large number of Firefox-controlling Selenium Remote Controls.