The NUnit 3 Test Adapter runs NUnit 3.x tests in Visual Studio 2012 and newer.
This adapter works with NUnit 3.0 and higher only. Use the NUnit 2 Adapter to run NUnit 2.x tests.
You can download the latest release version
or the latest pre-release version
Ask support questions 
The NUnit3TestAdapter wiki is the best place to start.
Also check the release notes.
The NUnit 3 Test Adapter is Open Source software released under the 
Visual Studio 2017 is the minimum required version to build the adapter.
Use .\build -t test at the command line to build and run complete tests.
To create a package use .\build -t package
To run and debug tests on .NET Framework, load DisableAppDomain.runsettings.
From Visual Studio 2019 version 16.2 preview 4 it is possible to run tests against a selected target framework in the test project, so one can use this to run .NET Core tests.
An alternative approach is to make use of the command line. If you need to frequently debug into .NET Core tests, you can temporarily switch the order of the <TargetFrameworks> in NUnit.TestAdapter.Tests.csproj.
The mock-assembly tests are not for direct running.
See https://github.com/nunit/docs/wiki/Packaging-the-V3-Adapter for more details.
The NuGet package and the VSIX contain source-linked PDBs for the adapter. If you’re in the middle of a debugging session and realize you’d like to be able to step into NUnit adapter code, set breakpoints and watch variables, follow these steps.
- From version 3.9 the NUnit3TestAdapter will stop supporting Visual Studio 2012 RTM (!), note only RTM, the later updates will still be supported fully. If you're using VS 2012 and want to update NUnit3TestAdapter, please update your Visual Studio RTM to any of the subsequent updates (Update 1-5)
- From version 3.16 the NUnit3TestAdapter will stop supporting .net core 1