Added a test class which shows the PriorityBlockingQueue being used

core-java/src/test/java/com/baeldung/concurrent/priorityblockingqueue/PriorityBlockingQueueUnitTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.concurrent.priorityblockingqueue;
+
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.concurrent.PriorityBlockingQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.IntStream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.util.Lists.newArrayList;
+
+public class PriorityBlockingQueueUnitTest {
+
+    @Test
+    public void shouldOrderQueue_whenPolling() throws InterruptedException {
+        PriorityBlockingQueue<Integer> queue = new PriorityBlockingQueue<>();
+        ArrayList<Integer> polledElements = new ArrayList<>();
+
+        queue.add(1);
+        queue.add(5);
+        queue.add(2);
+        queue.add(3);
+        queue.add(4);
+
+        polledElements.add(queue.poll());
+        polledElements.add(queue.poll());
+        polledElements.add(queue.poll());
+        polledElements.add(queue.poll());
+        polledElements.add(queue.poll());
+
+        assertThat(polledElements).containsExactly(1, 2, 3, 4, 5);
+    }
+
+    @Test
+    public void shouldBlockThread_WhenPollingEmptyQueue() throws InterruptedException {
+        PriorityBlockingQueue<Integer> queue = new PriorityBlockingQueue<>();
+
+        final Thread thread = new Thread(() -> {
+          System.out.println("Polling...");
+          while (true) {
+            try {
+              Integer poll = queue.take();
+              System.out.println("Polled: " + poll);
+            } catch (InterruptedException e) {}
+          }
+        });
+        thread.start();
+
+        Thread.sleep(TimeUnit.SECONDS.toMillis(5));
+        System.out.println("Adding to queue");
+
+        queue.addAll(newArrayList(1, 5, 6, 1, 2, 6, 7));
+        Thread.sleep(TimeUnit.SECONDS.toMillis(1));
+    }
+}