BAEL-1370 Added test to show usage of ArrayDeque. (#3128)

core-java/src/test/java/com/baeldung/arraydeque/ArrayDequeTest.java

@@ -0,0 +1,50 @@
+package com.baeldung.arraydeque;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+import static org.junit.Assert.*;
+import org.junit.Test;
+
+public class ArrayDequeTest {
+
+    @Test
+    public void whenOffer_addsAtLast() {
+        final Deque<String> deque = new ArrayDeque<>();
+
+        deque.offer("first");
+        deque.offer("second");
+
+        assertEquals("second", deque.getLast());
+    }
+
+    @Test
+    public void whenPoll_removesFirst() {
+        final Deque<String> deque = new ArrayDeque<>();
+
+        deque.offer("first");
+        deque.offer("second");
+
+        assertEquals("first", deque.poll());
+    }
+
+    @Test
+    public void whenPush_addsAtFirst() {
+        final Deque<String> deque = new ArrayDeque<>();
+
+        deque.push("first");
+        deque.push("second");
+
+        assertEquals("second", deque.getFirst());
+    }
+
+    @Test
+    public void whenPop_removesLast() {
+        final Deque<String> deque = new ArrayDeque<>();
+
+        deque.push("first");
+        deque.push("second");
+
+        assertEquals("second", deque.pop());
+    }
+}