If you write your tests with Ginkgo [0] its CLI can do this for you.

It also has nice facilities to quickly disable a test or portion of a test by prepending an X to the test function name, or to focus a test (only run that test) by prepending an F. It’s pretty nice.

[0]: https://onsi.github.io/ginkgo/

If it can watch files and trigger your app to boot it can certainly trigfer the test runner.

Yes, on .NET, Visual Studio Enterprise.

https://docs.microsoft.com/en-us/visualstudio/test/live-unit...

this is just a fancy description for a basic rollout system.