Bael 882 delay queue (#1792)

* BAEL-882 Delay_queue article code

* BAEL-882 Removed println

* BAEL-882 formatting

* BAEL-882 test ordered

core-java/src/test/java/com/baeldung/concurrent/delayqueue/DelayQueueTest.java

@@ -0,0 +1,78 @@
+package com.baeldung.concurrent.delayqueue;
+
+import org.junit.FixMethodOrder;
+import org.junit.Test;
+import org.junit.runners.MethodSorters;
+
+import java.util.concurrent.*;
+
+import static junit.framework.TestCase.assertEquals;
+
+@FixMethodOrder(MethodSorters.NAME_ASCENDING)
+public class DelayQueueTest {
+    @Test
+    public void givenDelayQueue_whenProduceElement_thenShouldConsumeAfterGivenDelay() throws InterruptedException {
+        //given
+        ExecutorService executor = Executors.newFixedThreadPool(2);
+        BlockingQueue<DelayObject> queue = new DelayQueue<>();
+        int numberOfElementsToProduce = 2;
+        int delayOfEachProducedMessageMilliseconds = 500;
+        DelayQueueConsumer consumer = new DelayQueueConsumer(queue, numberOfElementsToProduce);
+        DelayQueueProducer producer
+                = new DelayQueueProducer(queue, numberOfElementsToProduce, delayOfEachProducedMessageMilliseconds);
+
+        //when
+        executor.submit(producer);
+        executor.submit(consumer);
+
+        //then
+        executor.awaitTermination(5, TimeUnit.SECONDS);
+        executor.shutdown();
+        assertEquals(consumer.numberOfConsumedElements.get(), numberOfElementsToProduce);
+
+    }
+
+    @Test
+    public void givenDelayQueue_whenProduceElementWithHugeDelay_thenConsumerWasNotAbleToConsumeMessageInGivenTime() throws InterruptedException {
+        //given
+        ExecutorService executor = Executors.newFixedThreadPool(2);
+        BlockingQueue<DelayObject> queue = new DelayQueue<>();
+        int numberOfElementsToProduce = 1;
+        int delayOfEachProducedMessageMilliseconds = 10_000;
+        DelayQueueConsumer consumer = new DelayQueueConsumer(queue, numberOfElementsToProduce);
+        DelayQueueProducer producer
+                = new DelayQueueProducer(queue, numberOfElementsToProduce, delayOfEachProducedMessageMilliseconds);
+
+        //when
+        executor.submit(producer);
+        executor.submit(consumer);
+
+        //then
+        executor.awaitTermination(5, TimeUnit.SECONDS);
+        executor.shutdown();
+        assertEquals(consumer.numberOfConsumedElements.get(), 0);
+
+    }
+
+    @Test
+    public void givenDelayQueue_whenProduceElementWithNegativeDelay_thenConsumeMessageImmediately() throws InterruptedException {
+        //given
+        ExecutorService executor = Executors.newFixedThreadPool(2);
+        BlockingQueue<DelayObject> queue = new DelayQueue<>();
+        int numberOfElementsToProduce = 1;
+        int delayOfEachProducedMessageMilliseconds = -10_000;
+        DelayQueueConsumer consumer = new DelayQueueConsumer(queue, numberOfElementsToProduce);
+        DelayQueueProducer producer
+                = new DelayQueueProducer(queue, numberOfElementsToProduce, delayOfEachProducedMessageMilliseconds);
+
+        //when
+        executor.submit(producer);
+        executor.submit(consumer);
+
+        //then
+        executor.awaitTermination(1, TimeUnit.SECONDS);
+        executor.shutdown();
+        assertEquals(consumer.numberOfConsumedElements.get(), 1);
+
+    }
+}