A common question when testing mobile versions of websites with Rainforest is whether or not you should run the same test on both mobile and desktop platforms at the same time.
The answer focuses on the mobile v. desktop UI. If there aren't any elements between the two interfaces that would affect how a user would interact with site, feel free to run the test against both mobile and desktop browsers simultaneously.
If, however, your mobile site's UI differs significantly from your desktop site's UI, it is best to have independent groups of tests to cover the various versions of your app. Simply put, potential differences in a mobile versus a desktop UI may determine how a tester interacts with the site. This in turn may affect how a test must be written to fit the dynamics of the version of the site being tested.
For example, let's say a login button located in the top right hand corner on the desktop version is blue. Now imagine that the same function is accessed on the mobile site by first clicking an icon with three horizontal bars in the left hand corner of the page.
If a tester was instructed to login by clicking the blue "login" button and this test ran against both mobile and web browsers, the test against the mobile browser would fail, because of the UI differences between the mobile and desktop versions of the site.