MainActivityTest.kt

@Test
fun testOpenDetailsOnItemClick() {
    mockRepoUsers(1)

    activityRule.launchActivity(Intent())

    Espresso.onView(ViewMatchers.withId(R.id.recyclerView))
            .perform(RecyclerViewActions.actionOnItemAtPosition<RecyclerView.ViewHolder>(0, ViewActions.click()))

    val expectedText = "User 1: 100 pts"

    Espresso.onView(Matchers.allOf(ViewMatchers.withId(android.support.design.R.id.snackbar_text), ViewMatchers.withText(expectedText)))
            .check(ViewAssertions.matches(ViewMatchers.isDisplayed()));
}