From 75298bb3f4a4322cb15c3fd9bb981b40d8d158e9 Mon Sep 17 00:00:00 2001
From: Oleksandr Klymenko <alexanderklmn@gmail.com>
Date: Mon, 21 Jul 2025 17:58:22 +0200
Subject: [PATCH] testing: improving `DequeTest` (#6410)

* testing: improving DequeTest

* testing: redundant case

* testing: fix to many static imports

* testing: add more test cases

---------

Co-authored-by: Deniz Altunkapan <93663085+DenizAltunkapan@users.noreply.github.com>
---
 .../datastructures/queues/DequeTest.java      | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/src/test/java/com/thealgorithms/datastructures/queues/DequeTest.java b/src/test/java/com/thealgorithms/datastructures/queues/DequeTest.java
index 1244a2e26..34b1ea2e0 100644
--- a/src/test/java/com/thealgorithms/datastructures/queues/DequeTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/queues/DequeTest.java
@@ -87,4 +87,38 @@ class DequeTest {
         deque.addFirst(5);
         assertEquals("Head -> 5 <-> 10 <-> 20 <- Tail", deque.toString());
     }
+
+    @Test
+    void testAlternatingAddRemove() {
+        Deque<Integer> deque = new Deque<>();
+        deque.addFirst(1);
+        deque.addLast(2);
+        deque.addFirst(0);
+        assertEquals(0, deque.pollFirst());
+        assertEquals(2, deque.pollLast());
+        assertEquals(1, deque.pollFirst());
+        org.junit.jupiter.api.Assertions.assertTrue(deque.isEmpty());
+    }
+
+    @Test
+    void testSizeAfterOperations() {
+        Deque<Integer> deque = new Deque<>();
+        assertEquals(0, deque.size());
+        deque.addFirst(1);
+        deque.addLast(2);
+        deque.addFirst(3);
+        assertEquals(3, deque.size());
+        deque.pollFirst();
+        deque.pollLast();
+        assertEquals(1, deque.size());
+    }
+
+    @Test
+    void testNullValues() {
+        Deque<String> deque = new Deque<>();
+        deque.addFirst(null);
+        assertNull(deque.peekFirst());
+        assertNull(deque.pollFirst());
+        org.junit.jupiter.api.Assertions.assertTrue(deque.isEmpty());
+    }
 }