Update CreateAndDetectLoop with tests (#5561)

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

@@ -0,0 +1,71 @@
+package com.thealgorithms.datastructures.lists;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class CreateAndDetectLoopTest {
+
+    private CreateAndDetectLoop.Node head;
+
+    @BeforeEach
+    void setUp() {
+        // Create a linked list: 1 -> 2 -> 3 -> 4 -> 5 -> 6
+        head = new CreateAndDetectLoop.Node(1);
+        CreateAndDetectLoop.Node second = new CreateAndDetectLoop.Node(2);
+        CreateAndDetectLoop.Node third = new CreateAndDetectLoop.Node(3);
+        CreateAndDetectLoop.Node fourth = new CreateAndDetectLoop.Node(4);
+        CreateAndDetectLoop.Node fifth = new CreateAndDetectLoop.Node(5);
+        CreateAndDetectLoop.Node sixth = new CreateAndDetectLoop.Node(6);
+
+        head.next = second;
+        second.next = third;
+        third.next = fourth;
+        fourth.next = fifth;
+        fifth.next = sixth;
+    }
+
+    @Test
+    void testDetectLoopNoLoop() {
+        // Test when no loop exists
+        assertFalse(CreateAndDetectLoop.detectLoop(head), "There should be no loop.");
+    }
+
+    @Test
+    void testCreateAndDetectLoopLoopExists() {
+        // Create a loop between position 2 (node with value 2) and position 5 (node with value 5)
+        CreateAndDetectLoop.createLoop(head, 2, 5);
+
+        // Now test if the loop is detected
+        assertTrue(CreateAndDetectLoop.detectLoop(head), "A loop should be detected.");
+    }
+
+    @Test
+    void testCreateLoopInvalidPosition() {
+        // Create loop with invalid positions
+        CreateAndDetectLoop.createLoop(head, 0, 0);
+
+        // Ensure no loop was created
+        assertFalse(CreateAndDetectLoop.detectLoop(head), "There should be no loop with invalid positions.");
+    }
+
+    @Test
+    void testCreateLoopSelfLoop() {
+        // Create a self-loop at position 3 (node with value 3)
+        CreateAndDetectLoop.createLoop(head, 3, 3);
+
+        // Test if the self-loop is detected
+        assertTrue(CreateAndDetectLoop.detectLoop(head), "A self-loop should be detected.");
+    }
+
+    @Test
+    void testCreateLoopNoChangeForNonExistentPositions() {
+        // Create a loop with positions that don't exist in the linked list
+        CreateAndDetectLoop.createLoop(head, 10, 20);
+
+        // Ensure no loop was created
+        assertFalse(CreateAndDetectLoop.detectLoop(head), "No loop should be created if positions are out of bounds.");
+    }
+}