Add delaySubscription() methods to Completable #5081 (#6242)

* Add delaySubscription() methods to Completable #5081

* fix parameter test and documentation for delaySubscription()

* add tests to delayCompletable()

* remove mocked observer from delaySubscription() tests for Completable

src/main/java/io/reactivex/Completable.java

@@ -1390,6 +1390,51 @@ public final Completable delay(final long delay, final TimeUnit unit, final Sche
         return RxJavaPlugins.onAssembly(new CompletableDelay(this, delay, unit, scheduler, delayError));
     }
 
+    /**
+     * Returns a Completable that delays the subscription to the source CompletableSource by a given amount of time.
+     * <p>
+     * <dl>
+     *  <dt><b>Scheduler:</b></dt>
+     *  <dd>This version of {@code delaySubscription} operates by default on the {@code computation} {@link Scheduler}.</dd>
+     * </dl>
+     *
+     * @param delay the time to delay the subscription
+     * @param unit  the time unit of {@code delay}
+     * @return a Completable that delays the subscription to the source CompletableSource by the given amount
+     * @since 2.2.3 - experimental
+     * @see <a href="http://reactivex.io/documentation/operators/delay.html">ReactiveX operators documentation: Delay</a>
+     */
+    @CheckReturnValue
+    @Experimental
+    @SchedulerSupport(SchedulerSupport.COMPUTATION)
+    public final Completable delaySubscription(long delay, TimeUnit unit) {
+        return delaySubscription(delay, unit, Schedulers.computation());
+    }
+
+    /**
+     * Returns a Completable that delays the subscription to the source CompletableSource by a given amount of time,
+     * both waiting and subscribing on a given Scheduler.
+     * <p>
+     * <dl>
+     *  <dt><b>Scheduler:</b></dt>
+     *  <dd>You specify which {@link Scheduler} this operator will use.</dd>
+     * </dl>
+     *
+     * @param delay     the time to delay the subscription
+     * @param unit      the time unit of {@code delay}
+     * @param scheduler the Scheduler on which the waiting and subscription will happen
+     * @return a Completable that delays the subscription to the source CompletableSource by a given
+     * amount, waiting and subscribing on the given Scheduler
+     * @since 2.2.3 - experimental
+     * @see <a href="http://reactivex.io/documentation/operators/delay.html">ReactiveX operators documentation: Delay</a>
+     */
+    @CheckReturnValue
+    @Experimental
+    @SchedulerSupport(SchedulerSupport.CUSTOM)
+    public final Completable delaySubscription(long delay, TimeUnit unit, Scheduler scheduler) {
+        return Completable.timer(delay, unit, scheduler).andThen(this);
+    }
+
     /**
      * Returns a Completable which calls the given onComplete callback if this Completable completes.
      * <p>

src/test/java/io/reactivex/internal/operators/completable/CompletableDelayTest.java

@@ -20,11 +20,14 @@
 
 import org.junit.Test;
 
-import io.reactivex.*;
+import io.reactivex.CompletableSource;
+import io.reactivex.TestHelper;
+import io.reactivex.Completable;
 import io.reactivex.exceptions.TestException;
 import io.reactivex.functions.*;
 import io.reactivex.observers.TestObserver;
-import io.reactivex.schedulers.*;
+import io.reactivex.schedulers.Schedulers;
+import io.reactivex.schedulers.TestScheduler;
 
 public class CompletableDelayTest {
 
@@ -120,4 +123,69 @@ public void errorDelayed() {
 
         to.assertFailure(TestException.class);
     }
+
+    @Test
+    public void errorDelayedSubscription() {
+        TestScheduler scheduler = new TestScheduler();
+
+        TestObserver<Void> to = Completable.error(new TestException())
+                .delaySubscription(100, TimeUnit.MILLISECONDS, scheduler)
+                .test();
+
+        to.assertEmpty();
+
+        scheduler.advanceTimeBy(90, TimeUnit.MILLISECONDS);
+
+        to.assertEmpty();
+
+        scheduler.advanceTimeBy(15, TimeUnit.MILLISECONDS);
+
+        to.assertFailure(TestException.class);
+    }
+
+    @Test
+    public void errorDelayedSubscriptionDisposeBeforeTime() {
+        TestScheduler scheduler = new TestScheduler();
+
+        Completable result = Completable.complete()
+                .delaySubscription(100, TimeUnit.MILLISECONDS, scheduler);
+        TestObserver<Void> to = result.test();
+
+        to.assertEmpty();
+
+        scheduler.advanceTimeBy(90, TimeUnit.MILLISECONDS);
+        to.dispose();
+
+        scheduler.advanceTimeBy(15, TimeUnit.MILLISECONDS);
+
+        to.assertEmpty();
+    }
+
+    @Test
+    public void testDelaySubscriptionDisposeBeforeTime() {
+        TestScheduler scheduler = new TestScheduler();
+
+        Completable result = Completable.complete()
+                .delaySubscription(100, TimeUnit.MILLISECONDS, scheduler);
+        TestObserver<Void> to = result.test();
+
+        to.assertEmpty();
+        scheduler.advanceTimeBy(90, TimeUnit.MILLISECONDS);
+        to.dispose();
+        scheduler.advanceTimeBy(15, TimeUnit.MILLISECONDS);
+        to.assertEmpty();
+    }
+
+    @Test
+    public void testDelaySubscription() {
+        TestScheduler scheduler = new TestScheduler();
+        Completable result = Completable.complete()
+                .delaySubscription(100, TimeUnit.MILLISECONDS, scheduler);
+        TestObserver<Void> to = result.test();
+
+        scheduler.advanceTimeBy(90, TimeUnit.MILLISECONDS);
+        to.assertEmpty();
+        scheduler.advanceTimeBy(15, TimeUnit.MILLISECONDS);
+        to.assertResult();
+    }
 }

src/test/java/io/reactivex/validators/ParamValidationCheckerTest.java

@@ -261,6 +261,10 @@ public void checkParallelFlowable() {
         addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class));
         addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "delay", Long.TYPE, TimeUnit.class, Scheduler.class, Boolean.TYPE));
 
+        // negative time is considered as zero time
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class));
+        addOverride(new ParamOverride(Completable.class, 0, ParamMode.ANY, "delaySubscription", Long.TYPE, TimeUnit.class, Scheduler.class));
+
         // zero repeat is allowed
         addOverride(new ParamOverride(Completable.class, 0, ParamMode.NON_NEGATIVE, "repeat", Long.TYPE));