Running your tests in parallel means different things to different people, as follows:
Running all of your tests against multiple browsers at the same time
Running your tests against multiple instances of the same browser
Should we run our tests in parallel to increase coverage?
I'm sure that, when you are writing automated tests to make sure things work
with the website you are testing, you are initially told that your website has to
work on all browsers. The reality is that this is just not true. There are many browsers out there and it's just not feasible to support everything. For example, will your AJAX-intensive site that has the odd Flash object work in the Lynx browser?
Lynx is a text-based web browser that can be used in a Linux terminal window and was still in active development in 2014.
The next thing you will hear is, "OK, we will support every browser supported by Selenium". Again that's great but we have problems. Something that most people don't realize is that the core Selenium team's of cial browser support is the current browser version, and the previous version at the time of release of a version of Selenium. In practice it may well work on older browsers and the core team does
a lot of work to try and make sure they don't break support for older browsers. However if you want to run a series of tests on Internet Explorer 6, Internet Explorer 7, or even Internet Explorer 8, you are actually running tests against browsers that are not of cially supported by Selenium.