Introduced ability to override AndroidMainThreadFeatureScheduler via plugin

Author: LachlanMcKee

mvicore-android/build.gradle.kts

@@ -30,6 +30,7 @@ android {
     }
 
     testOptions {
+        unitTests.isReturnDefaultValues = true
         unitTests.all {
             it.useJUnitPlatform()
         }

mvicore-android/src/main/java/com/badoo/mvicore/android/AndroidMainThreadFeatureScheduler.kt

@@ -11,11 +11,29 @@ import io.reactivex.android.schedulers.AndroidSchedulers
  *
  * It also uses the 'isOnFeatureThread' field to avoid observing on the main thread if it is already
  * the current thread.
+ *
+ * To help facilitate testing, you can override the scheduler using
+ * [MviCoreAndroidPlugins.setMainThreadFeatureScheduler]
  */
-object AndroidMainThreadFeatureScheduler: FeatureScheduler {
+object AndroidMainThreadFeatureScheduler : FeatureScheduler {
+    private val featureSchedulerDelegate: FeatureScheduler
+        get() = MviCoreAndroidPlugins.mainThreadFeatureScheduler
+
     override val scheduler: Scheduler
-        get() = AndroidSchedulers.mainThread()
+        get() = featureSchedulerDelegate.scheduler
 
     override val isOnFeatureThread: Boolean
-        get() = Looper.myLooper() == Looper.getMainLooper()
+        get() = featureSchedulerDelegate.isOnFeatureThread
+
+    /**
+     * The default implementation of the [AndroidMainThreadFeatureScheduler] which delegates to the
+     * RxAndroid main thread scheduler
+     */
+    object Default : FeatureScheduler {
+        override val scheduler: Scheduler
+            get() = AndroidSchedulers.mainThread()
+
+        override val isOnFeatureThread: Boolean
+            get() = Looper.myLooper() == Looper.getMainLooper()
+    }
 }

mvicore-android/src/main/java/com/badoo/mvicore/android/MviCoreAndroidPlugins.kt

@@ -0,0 +1,25 @@
+package com.badoo.mvicore.android
+
+import com.badoo.mvicore.feature.FeatureScheduler
+
+/**
+ * Allows customisation of the MVICore Android integration.
+ */
+object MviCoreAndroidPlugins {
+    @Volatile
+    var mainThreadFeatureScheduler: FeatureScheduler = AndroidMainThreadFeatureScheduler.Default
+
+    /**
+     * Overrides the [AndroidMainThreadFeatureScheduler].
+     */
+    fun setMainThreadFeatureScheduler(schedulerProvider: () -> FeatureScheduler) {
+        mainThreadFeatureScheduler = schedulerProvider()
+    }
+
+    /**
+     * Resets the plugins back to the original state.
+     */
+    fun reset() {
+        mainThreadFeatureScheduler = AndroidMainThreadFeatureScheduler.Default
+    }
+}

mvicore-android/src/test/java/com/badoo/mvicore/android/lifecycle/AndroidMainThreadFeatureSchedulerTest.kt

@@ -0,0 +1,37 @@
+package com.badoo.mvicore.android.lifecycle
+
+import com.badoo.mvicore.android.AndroidMainThreadFeatureScheduler
+import com.badoo.mvicore.android.MviCoreAndroidPlugins
+import com.badoo.mvicore.feature.FeatureSchedulers
+import io.reactivex.android.schedulers.AndroidSchedulers
+import io.reactivex.schedulers.Schedulers
+import org.junit.jupiter.api.AfterEach
+import org.junit.jupiter.api.Assertions.assertSame
+import org.junit.jupiter.api.Test
+
+class AndroidMainThreadFeatureSchedulerTest {
+    @AfterEach
+    fun after() {
+        MviCoreAndroidPlugins.reset()
+    }
+
+    @Test
+    fun `GIVEN android main scheduler not overridden WHEN scheduler accessed THEN scheduler is android main thread scheduler`() {
+        assertSame(AndroidSchedulers.mainThread(), AndroidMainThreadFeatureScheduler.scheduler)
+    }
+
+    @Test
+    fun `GIVEN android main scheduler overridden with trampoline feature scheduler WHEN scheduler accessed THEN scheduler is trampoline scheduler`() {
+        MviCoreAndroidPlugins.setMainThreadFeatureScheduler { FeatureSchedulers.TrampolineFeatureScheduler }
+
+        assertSame(Schedulers.trampoline(), AndroidMainThreadFeatureScheduler.scheduler)
+    }
+
+    @Test
+    fun `GIVEN android main scheduler overridden with trampoline feature scheduler AND reset WHEN scheduler accessed THEN scheduler is android main thread scheduler`() {
+        MviCoreAndroidPlugins.setMainThreadFeatureScheduler { FeatureSchedulers.TrampolineFeatureScheduler }
+        MviCoreAndroidPlugins.reset()
+
+        assertSame(AndroidSchedulers.mainThread(), AndroidMainThreadFeatureScheduler.scheduler)
+    }
+}