Clarify unittest for observeOn with ImmediateScheduler

- spying was removed since it wasn't being used and ImmediateScheduler results in no scheduling being done.

Author: benjchristensen

rxjava-core/src/main/java/rx/operators/OperationObserveOn.java

@@ -67,14 +67,14 @@ public Subscription call(final Observer<T> observer) {
 
     public static class UnitTest {
 
+        /**
+         * This is testing a no-op path since it uses Schedulers.immediate() which will not do scheduling.
+         */
         @Test
         @SuppressWarnings("unchecked")
         public void testObserveOn() {
-
-            Scheduler scheduler = spy(OperatorTester.UnitTest.forwardingScheduler(Schedulers.immediate()));
-
             Observer<Integer> observer = mock(Observer.class);
-            Observable.create(observeOn(Observable.from(1, 2, 3), scheduler)).subscribe(observer);
+            Observable.create(observeOn(Observable.from(1, 2, 3), Schedulers.immediate())).subscribe(observer);
 
             verify(observer, times(1)).onNext(1);
             verify(observer, times(1)).onNext(2);