Added additional test to prove issue

rxjava-core/src/test/java/rx/ZipTests.java

@@ -15,6 +15,10 @@
  */
 package rx;
 
+import static org.junit.Assert.*;
+
+import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -31,6 +35,7 @@
 import rx.functions.Action1;
 import rx.functions.Func1;
 import rx.functions.Func2;
+import rx.functions.FuncN;
 import rx.observables.GroupedObservable;
 
 public class ZipTests {
@@ -91,6 +96,28 @@ public void testCovarianceOfZip() {
         Observable.<Movie, CoolRating, Result> zip(horrors, ratings, combine);
     }
 
+    /**
+     * Occasionally zip may be invoked with 0 observables. This blocks indefinitely instead
+     * of immediately invoking zip with 0 argument.
+     */
+    @Test(timeout = 5000)
+    public void nonBlockingObservable() {
+
+        final Object invoked = new Object();
+
+        Collection<Observable<Object>> observables = Collections.emptyList();
+
+        Observable<Object> result = Observable.zip(observables, new FuncN<Object>() {
+            @Override
+            public Object call(final Object... args) {
+                assertEquals("No argument should have been passed", 0, args.length);
+                return invoked;
+            }
+        });
+
+        assertSame(invoked, result.toBlockingObservable().last());
+    }
+
     Func2<Media, Rating, ExtendedResult> combine = new Func2<Media, Rating, ExtendedResult>() {
         @Override
         public ExtendedResult call(Media m, Rating r) {