[fenix] For https://github.com/mozilla-mobile/fenix/issues/26723 - Ensure wallpapers are set on the main thread

Using Dispatchers.IO allowed the observer to react faster to wallpaper state
updates but caused issues with updating the wallpaper in fragment layout.

Using Dispatchers.Main.immediate gives us a bit slower reaction time but still
faster than Dispatchers.Main and allows us to still execute before the fragment
is visible.

app/src/main/java/org/mozilla/fenix/home/WallpapersObserver.kt

@@ -39,7 +39,7 @@ class WallpapersObserver(
     @VisibleForTesting
     internal var observeWallpapersStoreSubscription: Store.Subscription<AppState, AppAction>? = null
     @VisibleForTesting
-    internal var wallpapersScope = CoroutineScope(Dispatchers.IO)
+    internal var wallpapersScope = CoroutineScope(Dispatchers.Main.immediate)
 
     init {
         observeWallpaperUpdates()
@@ -49,7 +49,7 @@ class WallpapersObserver(
      * Immediately apply the current wallpaper automatically adjusted to support
      * the current configuration - portrait or landscape.
      */
-    suspend fun applyCurrentWallpaper() {
+    fun applyCurrentWallpaper() {
         showWallpaper()
     }
 
@@ -69,7 +69,7 @@ class WallpapersObserver(
             if (currentValue.name != lastObservedValue?.name) {
                 lastObservedValue = currentValue
 
-                wallpapersScope.launch { showWallpaper(currentValue) }
+                showWallpaper(currentValue)
             }
         }.also {
             it.resume()
@@ -77,7 +77,8 @@ class WallpapersObserver(
     }
 
     @VisibleForTesting
-    internal suspend fun showWallpaper(wallpaper: Wallpaper = appStore.state.wallpaperState.currentWallpaper) {
+    internal fun showWallpaper(wallpaper: Wallpaper = appStore.state.wallpaperState.currentWallpaper) {
+        wallpapersScope.launch {
             when (wallpaper) {
                 // We only want to update the wallpaper when it's different from the default one
                 // as the default is applied already on xml by default.
@@ -86,6 +87,7 @@ class WallpapersObserver(
                 }
                 else -> {
                     val bitmap = wallpapersUseCases.loadBitmap(wallpaper)
+
                     bitmap?.let {
                         it.scaleToBottomOfView(wallpaperImageView)
                         wallpaperImageView.isVisible = true
@@ -93,4 +95,5 @@ class WallpapersObserver(
                 }
             }
         }
+    }
 }

app/src/test/java/org/mozilla/fenix/home/WallpapersObserverTest.kt

@@ -10,7 +10,6 @@ import androidx.core.view.isVisible
 import io.mockk.Called
 import io.mockk.Runs
 import io.mockk.coEvery
-import io.mockk.coVerify
 import io.mockk.every
 import io.mockk.just
 import io.mockk.mockk
@@ -18,10 +17,8 @@ import io.mockk.spyk
 import io.mockk.verify
 import kotlinx.coroutines.cancel
 import mozilla.components.support.test.libstate.ext.waitUntilIdle
-import mozilla.components.support.test.rule.MainCoroutineRule
-import mozilla.components.support.test.rule.runTestOnMain
 import org.junit.Assert.assertNotNull
-import org.junit.Rule
+import org.junit.Assert.assertTrue
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.mozilla.fenix.components.AppStore
@@ -32,9 +29,6 @@ import org.mozilla.fenix.wallpapers.WallpapersUseCases
 
 @RunWith(FenixRobolectricTestRunner::class)
 class WallpapersObserverTest {
-    @get:Rule
-    val coroutinesTestRule = MainCoroutineRule()
-
     @Test
     fun `WHEN the observer is created THEN start observing the store`() {
         val appStore: AppStore = mockk(relaxed = true) {
@@ -47,15 +41,15 @@ class WallpapersObserverTest {
     }
 
     @Test
-    fun `WHEN asked to apply the wallpaper THEN show it`() = runTestOnMain {
+    fun `WHEN asked to apply the wallpaper THEN show it`() {
         val appStore = AppStore()
         val observer = spyk(WallpapersObserver(appStore, mockk(), mockk())) {
-            coEvery { showWallpaper(any()) } just Runs
+            every { showWallpaper(any()) } just Runs
         }
 
         observer.applyCurrentWallpaper()
 
-        coVerify { observer.showWallpaper(any()) }
+        verify { observer.showWallpaper(any()) }
     }
 
     @Test
@@ -73,10 +67,10 @@ class WallpapersObserverTest {
     }
 
     @Test
-    fun `WHEN the wallpaper is updated THEN show the wallpaper`() = runTestOnMain {
+    fun `WHEN the wallpaper is updated THEN show the wallpaper`() {
         val appStore = AppStore()
         val observer = spyk(WallpapersObserver(appStore, mockk(relaxed = true), mockk(relaxed = true))) {
-            coEvery { showWallpaper(any()) } just Runs
+            every { showWallpaper(any()) } just Runs
         }
 
         // Ignore the call on the real instance and call again "observeWallpaperUpdates"
@@ -86,38 +80,38 @@ class WallpapersObserverTest {
         val newWallpaper: Wallpaper = mockk(relaxed = true)
         appStore.dispatch(UpdateCurrentWallpaper(newWallpaper))
         appStore.waitUntilIdle()
-        coVerify { observer.showWallpaper(newWallpaper) }
+        verify { observer.showWallpaper(newWallpaper) }
     }
 
     @Test
-    fun `WHEN the wallpaper is updated to a new one THEN show the wallpaper`() = runTestOnMain {
+    fun `WHEN the wallpaper is updated to a new one THEN show the wallpaper`() {
         val appStore = AppStore()
         val wallpapersUseCases: WallpapersUseCases = mockk {
             coEvery { loadBitmap(any()) } returns null
         }
         val observer = spyk(WallpapersObserver(appStore, wallpapersUseCases, mockk(relaxed = true))) {
-            coEvery { showWallpaper(any()) } just Runs
+            every { showWallpaper(any()) } just Runs
         }
 
         // Ignore the call on the real instance and call again "observeWallpaperUpdates"
         // on the spy to be able to verify the "showWallpaper" call in the spy.
         observer.observeWallpaperUpdates()
-        coVerify { observer.showWallpaper(Wallpaper.Default) }
+        verify { observer.showWallpaper(Wallpaper.Default) }
 
         val wallpaper: Wallpaper = mockk(relaxed = true)
         appStore.dispatch(UpdateCurrentWallpaper(wallpaper))
         appStore.waitUntilIdle()
-        coVerify { observer.showWallpaper(wallpaper) }
+        verify { observer.showWallpaper(wallpaper) }
     }
 
     @Test
-    fun `WHEN the wallpaper is updated to the current one THEN don't try showing the same wallpaper again`() = runTestOnMain {
+    fun `WHEN the wallpaper is updated to the current one THEN don't try showing the same wallpaper again`() {
         val appStore = AppStore()
         val wallpapersUseCases: WallpapersUseCases = mockk {
             coEvery { loadBitmap(any()) } returns null
         }
         val observer = spyk(WallpapersObserver(appStore, wallpapersUseCases, mockk(relaxed = true))) {
-            coEvery { showWallpaper(any()) } just Runs
+            every { showWallpaper(any()) } just Runs
         }
         // Ignore the call on the real instance and call again "observeWallpaperUpdates"
         // on the spy to be able to verify the "showWallpaper" call in the spy.
@@ -126,15 +120,15 @@ class WallpapersObserverTest {
         val wallpaper: Wallpaper = mockk(relaxed = true)
         appStore.dispatch(UpdateCurrentWallpaper(wallpaper))
         appStore.waitUntilIdle()
-        coVerify { observer.showWallpaper(wallpaper) }
+        verify { observer.showWallpaper(wallpaper) }
 
         appStore.dispatch(UpdateCurrentWallpaper(wallpaper))
         appStore.waitUntilIdle()
-        coVerify(exactly = 1) { observer.showWallpaper(wallpaper) }
+        verify(exactly = 1) { observer.showWallpaper(wallpaper) }
     }
 
     @Test
-    fun `GIVEN no wallpaper is provided WHEN asked to show the wallpaper THEN show the current one`() = runTestOnMain {
+    fun `GIVEN no wallpaper is provided WHEN asked to show the wallpaper THEN show the current one`() {
         val wallpaper: Wallpaper = mockk()
         val appStore: AppStore = mockk(relaxed = true) {
             every { state.wallpaperState.currentWallpaper } returns wallpaper
@@ -143,10 +137,10 @@ class WallpapersObserverTest {
 
         observer.showWallpaper()
 
-        coVerify { observer.showWallpaper(wallpaper) }
+        verify { observer.showWallpaper(wallpaper) }
     }
 
-    fun `GiVEN the current wallpaper is the default one WHEN showing it THEN hide the wallpaper view`() = runTestOnMain {
+    fun `GiVEN the current wallpaper is the default one WHEN showing it THEN hide the wallpaper view`() {
         val wallpapersUseCases: WallpapersUseCases = mockk()
         val wallpaperView: ImageView = mockk(relaxed = true)
         val observer = WallpapersObserver(mockk(relaxed = true), wallpapersUseCases, wallpaperView)
@@ -158,7 +152,7 @@ class WallpapersObserverTest {
     }
 
     @Test
-    fun `GiVEN the current wallpaper is different than the default one WHEN showing it THEN load it's bitmap in the visible wallpaper view`() = runTestOnMain {
+    fun `GiVEN the current wallpaper is different than the default one WHEN showing it THEN load it's bitmap in the visible wallpaper view`() {
         val wallpaper: Wallpaper = mockk()
         val bitmap: Bitmap = mockk()
         val wallpapersUseCases: WallpapersUseCases = mockk {
@@ -172,4 +166,16 @@ class WallpapersObserverTest {
         verify { wallpaperView.isVisible = true }
         verify { wallpaperView.setImageBitmap(bitmap) }
     }
+
+    @Test
+    fun `GIVEN the observer THEN use the main thread for showing the wallpaper`() {
+        val wallpapersUseCases: WallpapersUseCases = mockk()
+        val wallpaperView: ImageView = mockk(relaxed = true)
+
+        val observer = WallpapersObserver(mockk(relaxed = true), wallpapersUseCases, wallpaperView)
+
+        // Check that the context that would be used is Dispatchers.Main.immediate
+        // Unfortunately I could not also test that this is actually used when "showWallpaper" is called.
+        assertTrue(observer.wallpapersScope.toString().contains("Dispatchers.Main.immediate"))
+    }
 }