Test your app on foldables

The Jetpack WindowManager library notifies your application when there’s a change in the posture of a foldable device so that you can modify the application’s layout.

The Jetpack WindowManager window-testing artifact includes a WindowLayoutInfoPublisherRule JUnit4 rule that can publish a custom WindowInfoLayout to simulate a FoldingFeature in tests.

You can start by defining your test class and the testing rules:

import androidx.window.layout.FoldingFeature.Orientation.Companion.HORIZONTAL
import androidx.window.layout.FoldingFeature.Orientation.Companion.VERTICAL
import androidx.window.layout.FoldingFeature.State.Companion.FLAT
import androidx.window.layout.FoldingFeature.State.Companion.HALF_OPENED
import androidx.window.testing.layout.FoldingFeature
import androidx.window.testing.layout.TestWindowLayoutInfo
import androidx.window.testing.layout.WindowLayoutInfoPublisherRule

@RunWith(AndroidJUnit4::class)
class DisplayFeaturesActivityTest {
    private val activityRule = ActivityScenarioRule(DisplayFeaturesActivity::class.java)
    private val publisherRule = WindowLayoutInfoPublisherRule()

    @get:Rule
    val testRule: TestRule

    init {
        testRule = RuleChain.outerRule(publisherRule).around(activityRule)
    }

    @Test myTest() {
       // TODO
    }
}

import static androidx.window.layout.FoldingFeature.Orientation.HORIZONTAL;
import static androidx.window.layout.FoldingFeature.Orientation.VERTICAL;
import static androidx.window.layout.FoldingFeature.State.FLAT;
import static androidx.window.layout.FoldingFeature.State.HALF_OPENED;
import static androidx.window.testing.layout.DisplayFeatureTesting.createFoldingFeature;
import static androidx.window.testing.layout.WindowLayoutInfoTesting.createWindowLayoutInfo;
import androidx.window.layout.FoldingFeature;
import androidx.window.layout.WindowLayoutInfo;
import androidx.window.testing.layout.WindowLayoutInfoPublisherRule;

@RunWith(AndroidJUnit4.class)
public class DisplayFeaturesActivityJavaTest {
    private WindowLayoutInfoPublisherRule publisherRule = new WindowLayoutInfoPublisherRule();

    @Rule public TestRule testRule;

    public DisplayFeaturesActivityJavaTest() {
        testRule = RuleChain.outerRule(publisherRule).around(activityRule);
    };

     @Test
     public void myTest() {
         // TODO
     }
}

We can simulate a half-opened foldable screen with a centered horizontal fold of zero width with the code:

val feature = FoldingFeature(
                  activity = activity,
                  state = HALF_OPENED,
                  orientation = HORIZONTAL)

val expected = TestWindowLayoutInfo(listOf(feature))

FoldingFeature feature = createFoldingFeature(
                             activity,
                             -1,
                             0,
                             HALF_OPENED,
                             HORIZONTAL);

WindowLayoutInfo expected = createWindowLayoutInfo(
                                Collections.singletonList(feature)
                            );

then use the WindowLayoutInfoPublisherRule to publish it:

@Test
myTest() {
    ...
    publisherRule.overrideWindowLayoutInfo(expected)
    ...
}

@Test
public void myTest() {
    ...
    publisherRule.overrideWindowLayoutInfo(expected);
    ...
}

The final step is to check that the activity layout we're testing behaves as expected using the available Espresso matchers.

Below is an example of a test simulating a FoldingFeature with a HALF_OPENED vertical hinge in the screen’s center, and then using a matcher to check that the layout is the one we expect:

@Test
fun testDeviceOpen_Vertical() {
    activityRule.scenario.onActivity { activity ->
        val feature = FoldingFeature(
                          activity = activity,
                          state = HALF_OPENED,
                          orientation = VERTICAL)
        val expected = TestWindowLayoutInfo(listOf(feature))
        publisherRule.overrideWindowLayoutInfo(expected)
    }

    // Checks that start_layout is on the left of end_layout with a vertical folding feature.
    onView(withId(R.id.start_layout))
        .check(isCompletelyLeftOf(withId(R.id.end_layout)))
}

@Test
public void testDeviceOpen_Vertical() {
    activityRule
        .getScenario()
        .onActivity(
            activity -> {
                FoldingFeature feature = createFoldingFeature(
                                             activity,
                                             -1,
                                             0,
                                             HALF_OPENED,
                                             VERTICAL);

                WindowLayoutInfo expected = createWindowLayoutInfo(
                                                Collections.singletonList(feature)
                                            );

                publisherRule.overrideWindowLayoutInfo(expected);
            });

    // Checks that start_layout is on the left of end_layout with a vertical folding feature.
    onView(withId(R.id.start_layout))
        .check(isCompletelyLeftOf(withId(R.id.end_layout)));
}