Issue#84 Ensure BackgroundThread work is synced for DiffUtil

app/src/main/java/org/fnives/test/showcase/ui/home/FavouriteContentAdapter.kt

@@ -1,6 +1,7 @@
 package org.fnives.test.showcase.ui.home
 
 import android.view.ViewGroup
+import androidx.recyclerview.widget.AsyncDifferConfig
 import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.ListAdapter
 import org.fnives.test.showcase.R
@@ -8,13 +9,16 @@ import org.fnives.test.showcase.databinding.ItemFavouriteContentBinding
 import org.fnives.test.showcase.model.content.ContentId
 import org.fnives.test.showcase.model.content.FavouriteContent
 import org.fnives.test.showcase.ui.shared.ViewBindingAdapter
+import org.fnives.test.showcase.ui.shared.executor.AsyncTaskExecutor
 import org.fnives.test.showcase.ui.shared.layoutInflater
 import org.fnives.test.showcase.ui.shared.loadRoundedImage
 
 class FavouriteContentAdapter(
     private val listener: OnFavouriteItemClicked,
 ) : ListAdapter<FavouriteContent, ViewBindingAdapter<ItemFavouriteContentBinding>>(
-    DiffUtilItemCallback()
+    AsyncDifferConfig.Builder(DiffUtilItemCallback())
+        .setBackgroundThreadExecutor(AsyncTaskExecutor.iOThreadExecutor)
+        .build()
 ) {
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewBindingAdapter<ItemFavouriteContentBinding> =

app/src/main/java/org/fnives/test/showcase/ui/shared/executor/AsyncTaskExecutor.kt

@@ -0,0 +1,28 @@
+package org.fnives.test.showcase.ui.shared.executor
+
+import java.util.concurrent.Executor
+
+/**
+ * Basic copy of [ArchTaskExecutor][androidx.arch.core.executor.ArchTaskExecutor], needed because that is restricted to Library.
+ *
+ * Intended to be used for [AsyncDifferConfig][androidx.recyclerview.widget.AsyncDifferConfig] so it can be synchronized with Espresso.
+ *
+ * Workaround until https://github.com/android/android-test/issues/382 is fixed finally.
+ */
+object AsyncTaskExecutor : TaskExecutor {
+
+    val mainThreadExecutor = Executor { command -> postToMainThread(command) }
+    val iOThreadExecutor = Executor { command -> executeOnDiskIO(command) }
+
+    var delegate: TaskExecutor? = null
+    private val defaultExecutor by lazy { DefaultTaskExecutor() }
+    private val executor get() = delegate ?: defaultExecutor
+
+    override fun executeOnDiskIO(runnable: Runnable) {
+        executor.executeOnDiskIO(runnable)
+    }
+
+    override fun postToMainThread(runnable: Runnable) {
+        executor.postToMainThread(runnable)
+    }
+}

app/src/main/java/org/fnives/test/showcase/ui/shared/executor/DefaultTaskExecutor.kt

@@ -0,0 +1,34 @@
+package org.fnives.test.showcase.ui.shared.executor
+
+import android.os.Build
+import android.os.Handler
+import android.os.Looper
+import java.util.concurrent.Executors
+
+/**
+ * Basic copy of [androidx.arch.core.executor.DefaultTaskExecutor], needed because that is restricted to Library.
+ * With a Flavour of [androidx.recyclerview.widget.AsyncDifferConfig].
+ * Used within [AsyncTaskExecutor].
+ *
+ * Intended to be used for AsyncDiffUtil so it can be synchronized with Espresso.
+ */
+class DefaultTaskExecutor : TaskExecutor {
+
+    private val diskIO = Executors.newFixedThreadPool(2)
+    private val mMainHandler: Handler by lazy { createAsync(Looper.getMainLooper()) }
+
+    override fun executeOnDiskIO(runnable: Runnable) {
+        diskIO.execute(runnable)
+    }
+
+    override fun postToMainThread(runnable: Runnable) {
+        mMainHandler.post(runnable)
+    }
+
+    private fun createAsync(looper: Looper): Handler =
+        if (Build.VERSION.SDK_INT >= 28) {
+            Handler.createAsync(looper)
+        } else {
+            Handler(looper)
+        }
+}

app/src/main/java/org/fnives/test/showcase/ui/shared/executor/TaskExecutor.kt

@@ -0,0 +1,10 @@
+package org.fnives.test.showcase.ui.shared.executor
+
+/**
+ * Define TaskExecutor intended for [AsyncDifferConfig][androidx.recyclerview.widget.AsyncDifferConfig]
+ */
+interface TaskExecutor {
+    fun executeOnDiskIO(runnable: Runnable)
+
+    fun postToMainThread(runnable: Runnable)
+}

app/src/sharedTest/java/org/fnives/test/showcase/testutils/idling/AsyncDiffUtilInstantTestRule.kt

@@ -0,0 +1,32 @@
+package org.fnives.test.showcase.testutils.idling
+
+import org.fnives.test.showcase.ui.shared.executor.AsyncTaskExecutor
+import org.fnives.test.showcase.ui.shared.executor.TaskExecutor
+import org.junit.rules.TestRule
+import org.junit.runner.Description
+import org.junit.runners.model.Statement
+
+/**
+ * Similar Test Rule to InstantTaskExecutorRule just for the [AsyncTaskExecutor] to make AsyncDiffUtil synchronized.
+ */
+class AsyncDiffUtilInstantTestRule : TestRule {
+    override fun apply(base: Statement, description: Description): Statement =
+        object : Statement() {
+            @Throws(Throwable::class)
+            override fun evaluate() {
+                AsyncTaskExecutor.delegate = object : TaskExecutor {
+                    override fun executeOnDiskIO(runnable: Runnable) {
+                        runnable.run()
+                    }
+
+                    override fun postToMainThread(runnable: Runnable) {
+                        runnable.run()
+                    }
+                }
+
+                base.evaluate()
+
+                AsyncTaskExecutor.delegate = null
+            }
+        }
+}

app/src/sharedTest/java/org/fnives/test/showcase/ui/home/MainActivityInstrumentedTest.kt

@@ -8,6 +8,7 @@ import org.fnives.test.showcase.network.mockserver.ContentData
 import org.fnives.test.showcase.network.mockserver.scenario.content.ContentScenario
 import org.fnives.test.showcase.network.mockserver.scenario.refresh.RefreshTokenScenario
 import org.fnives.test.showcase.testutils.MockServerScenarioSetupResetingTestRule
+import org.fnives.test.showcase.testutils.idling.AsyncDiffUtilInstantTestRule
 import org.fnives.test.showcase.testutils.idling.MainDispatcherTestRule
 import org.fnives.test.showcase.testutils.idling.loopMainThreadFor
 import org.fnives.test.showcase.testutils.idling.loopMainThreadUntilIdleWithIdlingResources
@@ -37,6 +38,7 @@ class MainActivityInstrumentedTest : KoinTest {
     @JvmField
     val ruleOrder: RuleChain = RuleChain.outerRule(mockServerScenarioSetupTestRule)
         .around(mainDispatcherTestRule)
+        .around(AsyncDiffUtilInstantTestRule())
 
     @Before
     fun setup() {