added unit test

Author: albinsabu2023

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

@@ -1,6 +1,5 @@
 package com.thealgorithms.datastructures.lists;
 
-
 public class CreateAndDetectLoop {
 
     // Node class representing a single node in the linked list
@@ -15,7 +14,7 @@ public static class Node {
     }
 
     // Method to create a loop between two specific positions in the linked list
-    /**
+    /*
      *  Test case that shows the Cycle(loop) in a LinkedList
      *  Let's take this linked list:
      *  1->2->3->4->5->6

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

@@ -0,0 +1,70 @@
+package com.thealgorithms.datastructures.lists;
+
+import static org.junit.jupiter.api.Assertions.*;
+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 testDetectLoop_NoLoop() {
+        // Test when no loop exists
+        assertFalse(CreateAndDetectLoop.detectLoop(head), "There should be no loop.");
+    }
+
+    @Test
+    void testCreateAndDetectLoop_LoopExists() {
+        // 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 testCreateLoop_InvalidPosition() {
+        // 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 testCreateLoop_SelfLoop() {
+        // 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 testCreateLoop_NoChangeForNonExistentPositions() {
+        // 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.");
+    }
+}
+