test: CircleLinkedListTest (#5422)

* test: CircleLinkedListTest

* checkstyle: fix formatting

---------

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

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));
+    }
+}