BAEL-845 transfer queue (#1676)

* BAEL-845 tranferqueue article

* BAEL-845 m to m example

* BAEL-845 move code to test

* BAEL-845 use tryTransfer

* BAEL-845 proper if logic

core-java/src/test/java/com/baeldung/transferqueue/TransferQueueTest.java

@@ -0,0 +1,62 @@
+package com.baeldung.transferqueue;
+
+import org.junit.Test;
+
+import java.util.concurrent.*;
+
+public class TransferQueueTest {
+
+    @Test
+    public void givenTransferQueue_whenUseMultipleConsumersAndMultipleProducers_thenShouldProcessAllMessages() throws InterruptedException {
+        //given
+        TransferQueue<String> transferQueue = new LinkedTransferQueue<>();
+        ExecutorService exService = Executors.newFixedThreadPool(3);
+        Producer producer1 = new Producer(transferQueue, "1", 3);
+        Producer producer2 = new Producer(transferQueue, "2", 3);
+        Consumer consumer1 = new Consumer(transferQueue, "1", 3);
+        Consumer consumer2 = new Consumer(transferQueue, "2", 3);
+
+        //when
+        exService.execute(producer1);
+        exService.execute(producer2);
+        exService.execute(consumer1);
+        exService.execute(consumer2);
+
+        //then
+        exService.awaitTermination(10_000, TimeUnit.MILLISECONDS);
+        exService.shutdown();
+    }
+
+    @Test
+    public void givenTransferQueue_whenUseOneConsumerAndOneProducer_thenShouldProcessAllMessages() throws InterruptedException {
+        //given
+        TransferQueue<String> transferQueue = new LinkedTransferQueue<>();
+        ExecutorService exService = Executors.newFixedThreadPool(2);
+        Producer producer = new Producer(transferQueue, "1", 3);
+        Consumer consumer = new Consumer(transferQueue, "1", 3);
+
+        //when
+        exService.execute(producer);
+        exService.execute(consumer);
+
+        //then
+        exService.awaitTermination(5000, TimeUnit.MILLISECONDS);
+        exService.shutdown();
+    }
+
+    @Test
+    public void givenTransferQueue_whenUseOneProducerAndNoConsumers_thenShouldFailWithTimeout() throws InterruptedException {
+        //given
+        TransferQueue<String> transferQueue = new LinkedTransferQueue<>();
+        ExecutorService exService = Executors.newFixedThreadPool(2);
+        Producer producer = new Producer(transferQueue, "1", 3);
+
+        //when
+        exService.execute(producer);
+
+        //then
+        exService.awaitTermination(5000, TimeUnit.MILLISECONDS);
+        exService.shutdown();
+    }
+
+}