Selenium Grid

Selenium Grid allows you to,

  • Scale by distributing tests on several machines ( parallel execution )
  • Manage multiple environments from a central point, making it easy to run the tests against a vast combination of browsers / OS.
  • Minimize the maintenance time for the grid by allowing you to implement custom hooks to leverage virtual infrastructure for instance.

Grid Basics

Selenium Grid allows you run your tests on different machines against different browsers in parallel. That is, running multiple tests at the same time against different machines running different browsers and operating systems. Essentially, Selenium Grid support distributed test execution. It allows for running your tests in a distributed test execution environment.

Generally speaking, there’s two reasons why you might want to use Selenium-Grid.

  • To run your tests against multiple browsers, multiple versions of browser, and browsers running on different operating systems.
  • To reduce the time it takes for the test suite to complete a test pass.

What is Selenium Grid?

Selenium Grid is used to speed up the execution of a test pass by using multiple machines to run tests in parallel. For example, if you have a suite of 100 tests, but you set up Selenium Grid to support 4 different machines (VMs or separate physical machines) to run those tests, your test suite will complete in (roughly) one-fourth the time as it would if you ran your tests sequentially on a single machine. For large test suites, and long-running test suite such as those performing large amounts of data-validation, this can be a significant time-saver. Some test suites can take hours to run. Another reason to boost the time spent running the suite is to shorten the turnaround time for test results after developers check-in code for the AUT. Increasingly software teams practicing Agile software development want test feedback as immediately as possible as opposed to wait overnight for an overnight test pass.

Selenium Grid is also used to support running tests against multiple runtime environments, specifically, against different browsers at the same time. For example, a ‘grid’ of virtual machines can be setup with each supporting a different browser that the application to be tested must support. So, machine 1 has Internet Explorer 8, machine 2, Internet Explorer 9, machine 3 the latest Chrome, and machine 4 the latest Firefox. When the test suite is run, Selenium Grid receives each test-browser combination and assigns each test to run against it’s required browser.

In addition, one can have a grid of all the same browser, type and version. For instance, one could have a grid of 4 machines each running 3 instances of Firefox 12, allowing for a ‘server-farm’ (in a sense) of available Firefox instances. When the suite runs, each test is passed to Selenium-Grid which assigns the test to the next available Firefox instance. In this manner one gets test pass where conceivably 12 tests are all running at the same time in parallel, significantly reducing the time required to complete a test pass.

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