In order to run Instrumentation Tests from within Android Studio, I typically select \"Android Instrumentation Tests\" as the test artifact to be built, via the Build Varian
From what I see, in Android Studio 2.3.3, this option is gone 4 ever.
@markproxy: this because that feature is no longer experimental but is embedded in Android Studio as a feature, and there is no need to disable it, I suppose.
Here, for anyone needs, a link to the Android Unit Test guide: Getting Started with Testing (Instrumented Unit Tests included)