feat(*): Add WithIndex IEnumerable extension

UnitTests/IEnumerableExtensionTests.cs

@@ -0,0 +1,35 @@
+using NUnit.Framework;
+using Creek.HelpfulExtensions;
+using System.Collections.Generic;
+
+namespace UnitTests
+{
+    public class IEnumerableExtensionTests
+    {
+        [SetUp]
+        public void Setup()
+        {
+        }
+
+        [Test]
+        public void IsSubstringBetweenFirst()
+        {
+            List<int> list = new List<int>()
+            {
+                1,2,3,4,5,6,7,8,9
+            };
+
+            string indexString = string.Empty;
+            string valueString = string.Empty;
+
+            foreach (var (item, index) in list.WithIndex())
+            {
+                indexString += index;
+                valueString += item;
+            }
+
+            Assert.AreEqual("012345678", indexString);
+            Assert.AreEqual("123456789", valueString);
+        }
+    }
+}