Currently, when any of the tests fail, the whole build is marked as unstable without further incofmation (happens probably here) Now that there is a new API which passes more information about the failed step. That change is documented here. So the nunit plugin should be adjusted so that it can be displayed, where the build got unstable. In JUnit, this PR introduced this change. This PR might be used as idea on how to implement this.
I could probably do it myself and open a PR but I miss some more background. The biggest problem is that in nunit-plugin at the specific place, I only see a `build (Run<?, ?>)` object. And it is based on `SimpleBuildStep` where I do not see the `getContext` method to get the `node` where I should add the `addOrReplaceAction(new WarningAction(Result.UNSTABLE)`. If someone could give me some hints, I could create a PR myself for this.