I recently updated to Resharper 8, and when I tried to run a suite of projects. These tests contain two suites of integration tests that both use IISExpress to run a website
This has now been fixed in Resharper 8.0.2: http://youtrack.jetbrains.com/issue/RSRP-374143#comment=27-572929
Do not forget to tick new option ReSharper | Options | Tools | Unit Testing | "Use separate AppDomain for each assembly with test" to get it works.
i.e. There is now a new option in the Unit Testing settings.