added test case for codecov

DataStructures.Tests/LinkedList/CircularLinkedListTests.cs

@@ -90,6 +90,27 @@ public static void TestInsertAfterOnNonExistingValue()
         Assert.That("10", Is.EqualTo(GetDisplayOutput(cll).Trim()));
     }
 
+    [Test]
+    public static void TestInsertAfterTailNode()
+    {
+        var cll = new CircularLinkedList<int>();
+        cll.InsertAtEnd(10);  // tail -> 10
+        cll.InsertAtEnd(20);  // tail -> 20
+        cll.InsertAtEnd(30);  // tail -> 30
+
+        // Insert after the current tail (30)
+        cll.InsertAfter(30, 40);  // This should make 40 the new tail
+
+        // Now 40 should be the tail, and the list should be 10 20 30 40
+        Assert.That("10 20 30 40", Is.EqualTo(GetDisplayOutput(cll).Trim()));
+
+        // Additionally, assert that tail's Data is now 40
+        var tailField = typeof(CircularLinkedList<int>).GetField("tail", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
+        var tailNode = (CircularLinkedListNode<int>?)tailField?.GetValue(cll);
+        Assert.That(tailNode!.Data, Is.EqualTo(40));  // tail should now point to 40
+    }
+
+
     [Test]
     public static void TestDeleteNode()
     {