test: CircleLinkedListTest (#5422)

* test: CircleLinkedListTest

* checkstyle: fix formatting

---------

Co-authored-by: alxkm <alx@alx.com>

src/main/java/com/thealgorithms/datastructures/lists/CircleLinkedList.java

@@ -51,22 +51,25 @@ public class CircleLinkedList<E> {
         size++;
     }
 
-    // utility function for traversing the list
     public String toString() {
-        Node<E> p = head.next;
-        String s = "[ ";
-        while (p != head) {
-            s += p.value;
-            if (p != tail) {
-                s += " , ";
-            }
-            p = p.next;
+        if (size == 0) {
+            return "[]";
         }
-        return s + " ]";
+        StringBuilder sb = new StringBuilder("[ ");
+        Node<E> current = head.next;
+        while (current != head) {
+            sb.append(current.value);
+            if (current.next != head) {
+                sb.append(", ");
+            }
+            current = current.next;
+        }
+        sb.append(" ]");
+        return sb.toString();
     }
 
     public E remove(int pos) {
-        if (pos > size || pos < 0) {
+        if (pos >= size || pos < 0) {
             // catching errors
             throw new IndexOutOfBoundsException("position cannot be greater than size or negative");
         }
@@ -89,18 +92,4 @@ public class CircleLinkedList<E> {
         size--;
         return saved;
     }
-
-    public static void main(String[] args) {
-        CircleLinkedList<Integer> cl = new CircleLinkedList<>();
-        cl.append(12);
-        System.out.println(cl);
-        cl.append(23);
-        System.out.println(cl);
-        cl.append(34);
-        System.out.println(cl);
-        cl.append(56);
-        System.out.println(cl);
-        cl.remove(3);
-        System.out.println(cl);
-    }
 }

src/test/java/com/thealgorithms/datastructures/lists/CircleLinkedListTest.java

@@ -0,0 +1,78 @@
+package com.thealgorithms.datastructures.lists;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class CircleLinkedListTest {
+
+    @Test
+    public void testAppendAndSize() {
+        CircleLinkedList<Integer> list = new CircleLinkedList<>();
+        list.append(1);
+        list.append(2);
+        list.append(3);
+
+        assertEquals(3, list.getSize());
+        assertEquals("[ 1, 2, 3 ]", list.toString());
+    }
+
+    @Test
+    public void testRemove() {
+        CircleLinkedList<Integer> list = new CircleLinkedList<>();
+        list.append(1);
+        list.append(2);
+        list.append(3);
+        list.append(4);
+
+        assertEquals(2, list.remove(1));
+        assertEquals(3, list.remove(1));
+        assertEquals("[ 1, 4 ]", list.toString());
+        assertEquals(2, list.getSize());
+    }
+
+    @Test
+    public void testRemoveInvalidIndex() {
+        CircleLinkedList<Integer> list = new CircleLinkedList<>();
+        list.append(1);
+        list.append(2);
+
+        assertThrows(IndexOutOfBoundsException.class, () -> list.remove(2));
+        assertThrows(IndexOutOfBoundsException.class, () -> list.remove(-1));
+    }
+
+    @Test
+    public void testToStringEmpty() {
+        CircleLinkedList<Integer> list = new CircleLinkedList<>();
+        assertEquals("[]", list.toString());
+    }
+
+    @Test
+    public void testToStringAfterRemoval() {
+        CircleLinkedList<Integer> list = new CircleLinkedList<>();
+        list.append(1);
+        list.append(2);
+        list.append(3);
+        list.remove(1);
+
+        assertEquals("[ 1, 3 ]", list.toString());
+    }
+
+    @Test
+    public void testSingleElement() {
+        CircleLinkedList<Integer> list = new CircleLinkedList<>();
+        list.append(1);
+
+        assertEquals(1, list.getSize());
+        assertEquals("[ 1 ]", list.toString());
+        assertEquals(1, list.remove(0));
+        assertEquals("[]", list.toString());
+    }
+
+    @Test
+    public void testNullElement() {
+        CircleLinkedList<String> list = new CircleLinkedList<>();
+        assertThrows(NullPointerException.class, () -> list.append(null));
+    }
+}