A simple scenario to run test against a view in a isolated fragment container.

ViewScenario.kt

/**
 * Launches a [View] in an [ViewHostFragment] root view container (onCreateView).
 * [ViewHostFragment] is hosted by an empty [FragmentActivity] which will [instantiate]
 * the [Fragment] and waits for it to reach a resumed state.
 *
 * If your testing [View] has a dependency to specific theme such as [R.style.Theme_AppCompat],
 * use the theme ID parameter in [launchViewInFragment] method.
 *
 * Usage example:
 *
 * ```
 *   launchViewInFragment { Button(context) }
 *       .onFragment {
 *           onView(instanceOf(Button::class.java)).check(matches(not(isEnabled())))
 *       }
 * ```
 *
 * @param themeResId a style resource id to be set to the host [Activity]'s theme
 * @param instantiate method which will be used to instantiate the [View] when
 * [ViewHostFragment.onCreateView] is invoked.
 *
 * @see FragmentScenario for more details.
 */
fun <T : View> launchViewInFragment(
    @StyleRes themeResId: Int = R.style.FragmentScenarioEmptyFragmentActivityTheme,
    instantiate: ViewFactory<T>
): FragmentScenario<ViewHostFragment<T>> = launchFragmentInContainer(
    themeResId = themeResId,
    instantiate = { ViewHostFragment(instantiate) }
)

typealias ViewFactory<T> = (ViewBuilder) -> T

/**
 * Runs the function on the main thread in a blocking way.
 *
 * In the lambda you have access to the view that is tested
 */
fun <T : View> FragmentScenario<ViewHostFragment<T>>.onView(action: (T) -> Unit): FragmentScenario<ViewHostFragment<T>> {
    onFragment { fragment -> action(requireNotNull(fragment.viewInTest)) }
    return this
}

/**
 * An empty [Fragment]. This [Fragment] is used to host a [View] in [launchViewInFragment].
 *
 * @see [launchViewInFragment] for more details.
 */
class ViewHostFragment <T : View>(
    private val viewFactory: ViewFactory<T>
) : Fragment() {

    internal var viewInTest: T? = null

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        val args = ViewBuilder(requireContext(), inflater, container, savedInstanceState)
        return viewFactory(args).also { viewInTest = it }
    }

    override fun onDestroyView() {
        viewInTest = null
        super.onDestroyView()
    }
}

/**
 * [ViewBuilder] is a generic builder of [View]'s which will be invoked
 * when [ViewHostFragment.onViewCreated] is invoked.
 *
 * @see launchViewInFragment for more details.
 */
data class ViewBuilder internal constructor(
    val context: Context,
    val inflater: LayoutInflater,
    val container: ViewGroup? = null,
    val savedInstanceState: Bundle? = null
)