2.x: Add public constructor for TestScheduler that takes the time. (#5906)

* 2.x: Add public constructor for TestScheduler that takes the time.

* Wording.

Author: vanniktech

src/main/java/io/reactivex/schedulers/TestScheduler.java

@@ -35,6 +35,25 @@ public final class TestScheduler extends Scheduler {
     // Storing time in nanoseconds internally.
     volatile long time;
 
+    /**
+     * Creates a new TestScheduler with initial virtual time of zero.
+     */
+    public TestScheduler() {
+        // No-op.
+    }
+
+    /**
+     * Creates a new TestScheduler with the specified initial virtual time.
+     *
+     * @param delayTime
+     *          the point in time to move the Scheduler's clock to
+     * @param unit
+     *          the units of time that {@code delayTime} is expressed in
+     */
+    public TestScheduler(long delayTime, TimeUnit unit) {
+        time = unit.toNanos(delayTime);
+    }
+
     static final class TimedRunnable implements Comparable<TimedRunnable> {
 
         final long time;

src/test/java/io/reactivex/schedulers/TestSchedulerTest.java

@@ -253,5 +253,10 @@ public void workerDisposed() {
         assertTrue(w.isDisposed());
     }
 
-
+    @Test
+    public void constructorTimeSetsTime() {
+        TestScheduler ts = new TestScheduler(5, TimeUnit.SECONDS);
+        assertEquals(5, ts.now(TimeUnit.SECONDS));
+        assertEquals(5000, ts.now(TimeUnit.MILLISECONDS));
+    }
 }