testing: improve QueueTest (#6423)

* testing: improve QueueTest

* testing: fix test

src/test/java/com/thealgorithms/datastructures/queues/QueueTest.java

@@ -124,4 +124,204 @@ public class QueueTest {
         Assertions.assertThrows(IllegalArgumentException.class, () -> new Queue<>(0));
         Assertions.assertThrows(IllegalArgumentException.class, () -> new Queue<>(-5));
     }
+
+    @Test
+    void testCircularBehavior() {
+        // Test that queue behaves correctly after multiple insert/remove cycles
+        queue.insert(1);
+        queue.insert(2);
+        queue.insert(3);
+
+        // Remove all elements
+        queue.remove(); // removes 1
+        queue.remove(); // removes 2
+        queue.remove(); // removes 3
+
+        // Add elements again to test circular behavior
+        queue.insert(4);
+        queue.insert(5);
+        queue.insert(6);
+
+        Assertions.assertEquals(4, queue.peekFront());
+        Assertions.assertEquals(6, queue.peekRear());
+        Assertions.assertEquals(3, queue.getSize());
+        Assertions.assertTrue(queue.isFull());
+    }
+
+    @Test
+    void testMixedInsertRemoveOperations() {
+        // Test interleaved insert and remove operations
+        queue.insert(1);
+        queue.insert(2);
+
+        Assertions.assertEquals(1, queue.remove());
+        queue.insert(3);
+        queue.insert(4);
+
+        Assertions.assertEquals(2, queue.remove());
+        Assertions.assertEquals(3, queue.remove());
+
+        queue.insert(5);
+        queue.insert(6);
+
+        Assertions.assertEquals(4, queue.peekFront());
+        Assertions.assertEquals(6, queue.peekRear());
+        Assertions.assertEquals(3, queue.getSize());
+    }
+
+    @Test
+    void testSingleElementOperations() {
+        // Test operations with single element
+        queue.insert(42);
+
+        Assertions.assertEquals(42, queue.peekFront());
+        Assertions.assertEquals(42, queue.peekRear());
+        Assertions.assertEquals(1, queue.getSize());
+        Assertions.assertFalse(queue.isEmpty());
+        Assertions.assertFalse(queue.isFull());
+
+        Assertions.assertEquals(42, queue.remove());
+        Assertions.assertTrue(queue.isEmpty());
+        Assertions.assertEquals(0, queue.getSize());
+    }
+
+    @Test
+    void testNullValueHandling() {
+        // Test queue with null values (if supported)
+        Queue<String> stringQueue = new Queue<>(3);
+
+        Assertions.assertTrue(stringQueue.insert(null));
+        Assertions.assertTrue(stringQueue.insert("test"));
+        Assertions.assertTrue(stringQueue.insert(null));
+
+        Assertions.assertNull(stringQueue.peekFront());
+        Assertions.assertNull(stringQueue.peekRear());
+        Assertions.assertEquals(3, stringQueue.getSize());
+
+        Assertions.assertNull(stringQueue.remove());
+        Assertions.assertEquals("test", stringQueue.peekFront());
+    }
+
+    @Test
+    void testStringDataType() {
+        // Test queue with String data type
+        Queue<String> stringQueue = new Queue<>(2);
+        stringQueue.insert("first");
+        stringQueue.insert("second");
+
+        Assertions.assertEquals("first", stringQueue.peekFront());
+        Assertions.assertEquals("second", stringQueue.peekRear());
+    }
+
+    @Test
+    void testLargerCapacityQueue() {
+        // Test queue with larger capacity
+        Queue<Integer> largeQueue = new Queue<>(10);
+
+        // Fill the queue
+        for (int i = 1; i <= 10; i++) {
+            Assertions.assertTrue(largeQueue.insert(i));
+        }
+
+        Assertions.assertTrue(largeQueue.isFull());
+        Assertions.assertFalse(largeQueue.insert(11));
+
+        // Remove half the elements
+        for (int i = 1; i <= 5; i++) {
+            Assertions.assertEquals(i, largeQueue.remove());
+        }
+
+        Assertions.assertEquals(6, largeQueue.peekFront());
+        Assertions.assertEquals(10, largeQueue.peekRear());
+        Assertions.assertEquals(5, largeQueue.getSize());
+    }
+
+    @Test
+    void testQueueCapacityOne() {
+        // Test queue with capacity of 1
+        Queue<Integer> singleQueue = new Queue<>(1);
+
+        Assertions.assertTrue(singleQueue.isEmpty());
+        Assertions.assertFalse(singleQueue.isFull());
+
+        Assertions.assertTrue(singleQueue.insert(100));
+        Assertions.assertTrue(singleQueue.isFull());
+        Assertions.assertFalse(singleQueue.isEmpty());
+        Assertions.assertFalse(singleQueue.insert(200));
+
+        Assertions.assertEquals(100, singleQueue.peekFront());
+        Assertions.assertEquals(100, singleQueue.peekRear());
+
+        Assertions.assertEquals(100, singleQueue.remove());
+        Assertions.assertTrue(singleQueue.isEmpty());
+    }
+
+    @Test
+    void testQueueWraparoundIndexing() {
+        // Test that internal array indexing wraps around correctly
+        queue.insert(1);
+        queue.insert(2);
+        queue.insert(3); // Queue full
+
+        // Remove one element
+        queue.remove(); // removes 1
+
+        // Add another element (should wrap around)
+        queue.insert(4);
+
+        Assertions.assertEquals("[2, 3, 4]", queue.toString());
+        Assertions.assertEquals(2, queue.peekFront());
+        Assertions.assertEquals(4, queue.peekRear());
+
+        // Continue the pattern
+        queue.remove(); // removes 2
+        queue.insert(5);
+
+        Assertions.assertEquals(3, queue.peekFront());
+        Assertions.assertEquals(5, queue.peekRear());
+    }
+
+    @Test
+    void testQueueStateAfterMultipleCycles() {
+        // Test queue state after multiple complete fill/empty cycles
+        for (int cycle = 0; cycle < 3; cycle++) {
+            // Fill the queue
+            for (int i = 1; i <= 3; i++) {
+                queue.insert(i + cycle * 10);
+            }
+
+            // Verify state
+            Assertions.assertTrue(queue.isFull());
+            Assertions.assertEquals(3, queue.getSize());
+
+            // Empty the queue
+            for (int i = 1; i <= 3; i++) {
+                queue.remove();
+            }
+
+            // Verify empty state
+            Assertions.assertTrue(queue.isEmpty());
+            Assertions.assertEquals(0, queue.getSize());
+        }
+    }
+
+    @Test
+    void testQueueConsistencyAfterOperations() {
+        // Test that queue maintains consistency after various operations
+        queue.insert(10);
+        queue.insert(20);
+
+        int firstRemoved = queue.remove();
+        queue.insert(30);
+        queue.insert(40);
+
+        int secondRemoved = queue.remove();
+        queue.insert(50);
+
+        // Verify the order is maintained
+        Assertions.assertEquals(10, firstRemoved);
+        Assertions.assertEquals(20, secondRemoved);
+        Assertions.assertEquals(30, queue.peekFront());
+        Assertions.assertEquals(50, queue.peekRear());
+    }
 }