Jetpack AndroidX Test "Write Once, Run Everywhere" - But What is the best way to run Everywhere?

Recently I show one of the google IO video about androidX testing which quote "Write Once, Run EveryWhere". Which makes me exciting to learn about androidX testing library.

And what I found that After long time google come up with the nice single library for Unit test and Instrumentation test for on/off devices. But I found some difficulties to run the same test on/off devices.

Basically In Android, We create two source root test/java and androidTest/java in which we store Unit test and Instrumentation test respectively. Unit test runs on JVM and Instrumentation run on device/simulation.

Then I wrote test for one of the fragment inside test/java directory.

@RunWith(AndroidJUnit4::class)
class MyFragmenTest {

    lateinit var scenario: FragmentScenario<MyFragment>

    @Before
    fun setUp() {
        scenario = launchFragmentInContainer<MyFragment>()
    }

    @Test
    fun `sample test`() {
        scenario.onFragment {
           // something 
        }

        // some assertion
    }
}

So When I execute this test using small green run icon, it run this test in JVM without emulator which is great. But to run the same test on device I have to move this code androidTest/java source root.

Basically I got that same test can run everywhere you don't have to rely on different tool & library for the same work when we use androidX testing library.

What I tried.

After, Searching on google I found that we have to create the sharedTest/java source root using below gradle line so that it can run both on or off device.

android {
    ...  
    sourceSets {
        androidTest {
            java.srcDirs += "src/sharedTest/java"
        }
        test {
            java.srcDirs += "src/sharedTest/java"
        }
    }
}

After placing my code into sharedTest/java and if I execute test using green run icon it always ask for device. Which is also confusing because I can never run this on JVM.

Here comes my question.

How to execute same test seamlessly on/off device without moving code to different source root?

from Jetpack AndroidX Test "Write Once, Run Everywhere" - But What is the best way to run Everywhere?