Fragment test example, using AndroidX

FragmentTestWithAndroidX.kt

private lateinit var scenario: FragmentScenario<SearchFragment>
private val parentActivity = mock<SearchFragment.ParentActivity>()

@Before
fun setUp() {
  // Prepare fake data for SearchFragment
  // ...

  // Setup the FragmentScenario and attach any required mock data to it
  scenario = launchFragmentInContainer<SearchFragment>(Bundle.EMPTY, R.style.Theme_AppCompat_Light)
  scenario.onFragment {
      it.setParentActivity(parentActivity)
  }
}

@Test
fun `when loading, progressbar is displayed`() {
  whenSearchReturns(Single.never())

  scenario.onFragment {
    it.performQuery("brexit")

    it.progressBar().shouldBeVisible()
  }
}

/////////////////////////////////////////////////////////////////

private fun whenSearchReturns(singleResult: Single<List<Tag>>) {
  given(searchRequest.execute(any())).willReturn(singleResult)
}

private fun SearchFragment.performQuery(query: String) {
  searchView()
    .setQuery(query, true)
}

// Or, if you declare these Views in the fragment w/ package-protected level, 
// you can call those fields directly.
private fun SearchFragment.searchView() = 
  view!!.findViewById<SearchView>(R.id.search_card_view_search_view)

private fun SearchFragment.progressBar() = 
  view!!.findViewById<View>(R.id.fragment_search_progress_bar)

private fun View.shouldBeVisible() {
    visibility shouldEqualTo View.VISIBLE
}