Windows phone 8.1 RT - ViewModel Unit Test - Mocking Framework

Question

I have Windows phone 8.1 RT app. I want to write ViewModel Unit test. So I have created Windows phone Unit test project.

I can't able install any Mocking framework like NSubstitute, Moq..

If i create General Unit test project, I can able to install the NSubstitute, but i couldn't refer the Windows phone 8.1 project because TargetFramework of Unit Test project is .Net framework 4.5.2.

Please help me to test my ViewModel using Mocking framework.

Thank you,