Is it a VS 2015 bug or a NuGet one - there are so many weird bugs whenever NuGet is used to install packages!
One such bug can be replicated by following the below bullet-ed steps:
- Install NUnitTestAdapter with NUGet (not the one with the WithFramework) in your NUnit test project. Set the test project's target framework version to "4.5"
- Check the Test Explorer and the target framework Settings of the project to ensure both synchronize.
- Add another project (say, for example, a class library to be tested from your NUnit test project). Set your project's target framework version to "4.5.2"
- Add reference to NUnit v2.6.4 (not v3.0 and not through NUGet) after downloading it from NUnit dot org and add some tests in your test project.
- Build solution. You should see some warnings as below.