A customer got this to my attention today.
The test adapter ('Microsoft.VisualStudio.TestTools.TestTypes.Unit.UnitTestAdapter, Microsoft.VisualStudio.QualityTools.Tips.UnitTest.Adapter, Version=18.104.22.168, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a') required to execute this test could not be loaded. Check that the test adapter is installed properly. Exception of type 'Microsoft.VisualStudio.SmartDevice.TestHostAdapter.DeviceAgent.NetCFNotInstalledException' was thrown.
The most common reason for this is if you are running a test on the emulator on which you don't have .NETCF 2.0 or 3.5 already installed. A simple workaround is to create a Smart Device Application and F5 it to deploy to the emulator before you run unit tests.
What I also do on my machine is that I have deployed .NETCF 2.0 and 3.5 to my emulators and Saved States. That way every time my emulator loads, Visual Studio does not have to push .NETCF over to the emulator. Make a considerable improvement in deploy Speed.