Adds DelegateExtensions + Tests which is used for retrying and is used with the Examine Index Sync

src/Umbraco.Tests/DelegateExtensionsTests.cs

@@ -0,0 +1,46 @@
+using System;
+using Lucene.Net.Index;
+using NUnit.Framework;
+using Umbraco.Core;
+
+namespace Umbraco.Tests
+{
+    [TestFixture]
+    public class DelegateExtensionsTests
+    {
+
+        [Test]
+        public void Only_Executes_Specific_Count()
+        {
+            var maxTries = 5;
+            var totalTries = 0;
+            DelegateExtensions.RetryUntilSuccessOrMaxAttempts((currentTry) =>
+            {
+                totalTries = currentTry;
+                return Attempt<IndexWriter>.Fail();
+            }, 5, TimeSpan.FromMilliseconds(10));
+
+            Assert.AreEqual(maxTries, totalTries);
+        }
+
+        [Test]
+        public void Quits_On_Success_Count()
+        {
+            var maxTries = 5;
+            var totalTries = 0;
+            DelegateExtensions.RetryUntilSuccessOrMaxAttempts((currentTry) =>
+            {
+                totalTries = currentTry;
+                if (totalTries == 2)
+                {
+                    return Attempt<string>.Succeed();
+                }                
+                return Attempt<string>.Fail();
+            }, 5, TimeSpan.FromMilliseconds(10));
+
+            Assert.AreEqual(2, totalTries);
+        }
+
+
+    }
+}