In this page of ReSharper options, you can adjust unit testing settings related to NUnit tests.
|Enable NUnit support||Enables or disables support of NUnit tests.|
|Run tests with:||ReSharper bundles and supports the last version of NUnit. If you want to use some version of NUnit other than 2.6, click Specified NUnit installation, then enter the path to the test framework into the corresponding text box (for example, 'C:\Program Files (x86)\NUnit 2.5.10\bin\net-2.0\lib').|
|Load NUnit Addins||Clicking the corresponding radio button, you specify whether to load NUnit addins or not, or load when it's required.|
ReSharper's settings are saved in settings layers that enable you to have different settings for different solutions as well as to share your settings with your team. To learn more, study the Managing and Sharing Options section.