Add AndroidSchedulers.reset() for better testing support

rxandroid/src/main/java/rx/android/schedulers/AndroidSchedulers.java

@@ -14,16 +14,33 @@
 package rx.android.schedulers;
 
 import android.os.Looper;
+
+import java.util.concurrent.atomic.AtomicReference;
+
 import rx.Scheduler;
 import rx.android.plugins.RxAndroidPlugins;
 import rx.android.plugins.RxAndroidSchedulersHook;
+import rx.annotations.Experimental;
 
 /** Android-specific Schedulers. */
 public final class AndroidSchedulers {
-    private static final AndroidSchedulers INSTANCE = new AndroidSchedulers();
+    private static final AtomicReference<AndroidSchedulers> INSTANCE = new AtomicReference<>();
 
     private final Scheduler mainThreadScheduler;
 
+    private static AndroidSchedulers getInstance() {
+        for (;;) {
+            AndroidSchedulers current = INSTANCE.get();
+            if (current != null) {
+                return current;
+            }
+            current = new AndroidSchedulers();
+            if (INSTANCE.compareAndSet(null, current)) {
+                return current;
+            }
+        }
+    }
+
     private AndroidSchedulers() {
         RxAndroidSchedulersHook hook = RxAndroidPlugins.getInstance().getSchedulersHook();
 
@@ -37,12 +54,22 @@ private AndroidSchedulers() {
 
     /** A {@link Scheduler} which executes actions on the Android UI thread. */
     public static Scheduler mainThread() {
-        return INSTANCE.mainThreadScheduler;
+        return getInstance().mainThreadScheduler;
     }
 
     /** A {@link Scheduler} which executes actions on {@code looper}. */
     public static Scheduler from(Looper looper) {
         if (looper == null) throw new NullPointerException("looper == null");
         return new LooperScheduler(looper);
     }
+
+    /**
+     * Resets the current {@link AndroidSchedulers} instance.
+     * This will re-init the cached schedulers on the next usage,
+     * which can be useful in testing.
+     */
+    @Experimental
+    public static void reset() {
+        INSTANCE.set(null);
+    }
 }

rxandroid/src/test/java/rx/android/schedulers/ResetSchedulersTest.java

@@ -0,0 +1,55 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.android.schedulers;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+import rx.Scheduler;
+import rx.android.plugins.RxAndroidPlugins;
+import rx.android.plugins.RxAndroidSchedulersHook;
+import rx.schedulers.TestScheduler;
+
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+@RunWith(RobolectricTestRunner.class)
+@Config(manifest = Config.NONE)
+public final class ResetSchedulersTest {
+
+    @Test
+    public void reset() {
+        RxAndroidPlugins.getInstance().reset();
+
+        final TestScheduler testScheduler = new TestScheduler();
+        RxAndroidPlugins.getInstance().registerSchedulersHook(new RxAndroidSchedulersHook() {
+            @Override
+            public Scheduler getMainThreadScheduler() {
+                return testScheduler;
+            }
+        });
+        AndroidSchedulers.reset();
+
+        assertSame(AndroidSchedulers.mainThread(), testScheduler);
+
+        RxAndroidPlugins.getInstance().reset();
+        RxAndroidPlugins.getInstance().registerSchedulersHook(RxAndroidSchedulersHook.getDefaultInstance());
+        AndroidSchedulers.reset();
+
+        assertTrue(AndroidSchedulers.mainThread() instanceof LooperScheduler);
+    }
+
+}