I opened Habitat.TestScenarios.sln solution and noticed my visual studio 2015 test explorer is sad and empty.
however when I tried ReSharper I could run tests with it after installing "xUnit.net Test support for resharper". You can install it easily by going to Resharper and then extension manger in visual studio.
To get list of your tests into Visual studio Test Explorer window you need to add "xunit.runner.visualstudio" nuget package to your projects. you can easily add it by right clicking on your solution and selecting "Manage NuGet Packages for solution" and then in Browse tab search for "xunit.runner.visualstudio" and select all the sitecore feature projects and select install.
after that you should be able to see list of tests.