Build and run unit-tests with two distinct jobs
You could use the Copy Artifact Plugin to copy the artefacts to another job and then run the unit tests but this may not work, depending on how C# handles packaging and the project is structured.
It look like you can use the NUint Plugin to publish the results of your tests so you may be able to use a single job as I don't think that the tests will run if the previous build step fails as they don't for JUnit tests