Provide Observable.timestamp(Scheduler) to be used in the tests.

Author: vigdorchik

language-adaptors/rxjava-scala/src/main/scala/rx/lang/scala/Observable.scala

@@ -281,6 +281,21 @@ trait Observable[+T]
       .map((t: rx.util.Timestamped[_ <: T]) => (t.getTimestampMillis, t.getValue))
   }
 
+  /**
+   * Wraps each item emitted by a source Observable in a timestamped tuple
+   * with timestamps provided by the given Scheduler.
+   * <p>
+   * <img width="640" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/timestamp.s.png">
+   * 
+   * @param scheduler [[rx.lang.scala.Scheduler]] to use as a time source.
+   * @return an Observable that emits timestamped items from the source
+   *         Observable with timestamps provided by the given Scheduler
+   */
+  def timestamp(scheduler: Scheduler): Observable[(Long, T)] = {
+    toScalaObservable[rx.util.Timestamped[_ <: T]](asJavaObservable.timestamp(scheduler))
+      .map((t: rx.util.Timestamped[_ <: T]) => (t.getTimestampMillis, t.getValue))
+  }
+
   /**
    * Returns an Observable formed from this Observable and another Observable by combining 
    * corresponding elements in pairs. 

language-adaptors/rxjava-scala/src/test/scala/rx/lang/scala/ObservableTest.scala

@@ -15,6 +15,7 @@
  */
 package rx.lang.scala
 
+import scala.collection.mutable.ListBuffer
 import scala.concurrent.{Future, Await}
 import scala.concurrent.duration.Duration
 import scala.concurrent.ExecutionContext.Implicits.global
@@ -123,6 +124,21 @@ class ObservableTests extends JUnitSuite {
     assertEquals(6, o.toBlockingObservable.single)
   }
 
+  @Test def testTimestampWithScheduler() {
+    val c = 10
+    val s = TestScheduler()
+    val o1 = Observable interval (1.milliseconds, s) map (_ + 1)
+    val o2 = o1 timestamp s
+    val l = ListBuffer[(Long, Long)]()
+    o2.subscribe (
+      onNext = (l += _)
+    )
+    s advanceTimeTo c.milliseconds
+    val (l1, l2) = l.toList.unzip
+    assertTrue(l1.size == c)
+    assertEquals(l2, l1)
+  }
+
   /*
  @Test def testHead() {
    val observer = mock(classOf[Observer[Int]])