Unable to add a reference to unit test project

Question

I am setting up a unit test bench and as an example exercise created a simple calculator. I'd like to develop test cases for it. When I try to add the project reference to the unit test project an error "Enable to add a reference to project 'Calculator'" appears. No reason or corrective action is provided

Initially I thought the reason was because developer mode was not enabled on my computer. But the problem persists with developer mode on also.

Answer 1

This issue has been resolved. I created a unit test project in .net instead of universal windows application and it worked