visual studio 2015 doesn't see my xunit tests

I have had the same problem today. This solution works for me:

"dependencies": {
    "xunit": "2.1.0-beta3-*",
    "xunit.runner.dnx": "2.1.0-beta3-*",
    "xunit.runner.visualstudio": "2.1.0",
    "xunit.runners": "2.0.0"
  },
"commands": {
    "test": "xunit.runner.dnx"
  },

I hope this help you. I had to install 3 nuget package: xunit, xunit.runner.visualstudio and xunit.runners