Starting from Visual Studio 2012 the testing infrastructure became extensible making it possible to add support for other test frameworks without the need of 3th party plugins like Resharper or Gallio.
Just before the year ended, the NUnit team released a new version(beta 4) of their NUnit Test Adapter for Visual Studio, with support for VS 2012 Update 1. The new release, version 0.94, works with the VS 2012 RTM as well but shows off some extra features when used with the update.
The biggest addition to the Adapter in this release is that it now supports Traits. NUnit Properties and Categories are translated in to Visual Studio traits and you can sort the display of tests by trait or filter on them. This goes a long way toward making the Visual Studio Test Explorer useful in running large sets of tests.
Release notes for this version can be found here: http://nunit.org/index.php?p=vsTestAdapterReleaseNotes&r=2.6.2
More information about Traits here: http://blogs.msdn.com/b/visualstudioalm/archive/2012/11/09/how-to-manage-unit-tests-in-visual-studio-2012-update-1-part-1-using-traits-in-the-unit-test-explorer.aspx