diff --git a/X10D.Tests/src/Core/StringTests.cs b/X10D.Tests/src/Core/StringTests.cs
index 32d6fb4..6d58576 100644
--- a/X10D.Tests/src/Core/StringTests.cs
+++ b/X10D.Tests/src/Core/StringTests.cs
@@ -9,6 +9,30 @@
     [TestClass]
     public class StringTests
     {
+        /// <summary>
+        ///     Tests for <see cref="StringExtensions.AsNullIfEmpty" />.
+        /// </summary>
+        [TestMethod]
+        public void AsNullIfEmpty()
+        {
+            Assert.AreEqual(null, string.Empty.AsNullIfEmpty());
+            Assert.AreEqual(null, ((string)null).AsNullIfEmpty());
+            Assert.AreEqual("   ", "   ".AsNullIfEmpty());
+            Assert.AreEqual("foo", "foo".AsNullIfEmpty());
+        }
+
+        /// <summary>
+        ///     Tests for <see cref="StringExtensions.AsNullIfWhiteSpace" />.
+        /// </summary>
+        [TestMethod]
+        public void AsNullIfWhiteSpace()
+        {
+            Assert.AreEqual(null, string.Empty.AsNullIfWhiteSpace());
+            Assert.AreEqual(null, ((string)null).AsNullIfWhiteSpace());
+            Assert.AreEqual(null, "   ".AsNullIfWhiteSpace());
+            Assert.AreEqual("foo", "foo".AsNullIfWhiteSpace());
+        }
+
         /// <summary>
         ///     Tests for <see cref="StringExtensions.Repeat" />.
         /// </summary>
@@ -18,6 +42,16 @@
             Assert.AreEqual("foofoofoofoofoo", "foo".Repeat(5));
         }
 
+        /// <summary>
+        ///     Tests for <see cref="StringExtensions.Reverse" />.
+        /// </summary>
+        [TestMethod]
+        public void Reverse()
+        {
+            Assert.AreEqual("dlroW olleH", StringExtensions.Reverse("Hello World"));
+            Assert.AreEqual("Foobar", StringExtensions.Reverse("rabooF"));
+        }
+
         /// <summary>
         ///     Tests for <see cref="StringExtensions.Split" />.
         /// </summary>
@@ -30,5 +64,18 @@
             var arr = str.Split(2).ToArray();
             CollectionAssert.AreEqual(new[] { "He", "ll", "o ", "Wo", "rl", "d" }, arr);
         }
+
+        /// <summary>
+        ///     Tests for <see cref="StringExtensions.WithAlternative" />.
+        /// </summary>
+        [TestMethod]
+        public void WithAlternative()
+        {
+            Assert.AreEqual("Hello", "Hello".WithAlternative("Discarded"));
+            Assert.AreEqual("Alternative", string.Empty.WithAlternative("Alternative"));
+            Assert.AreEqual("   ", "   ".WithAlternative("Discarded"));
+            Assert.AreEqual("Alternative", "   ".WithAlternative("Alternative", true));
+            Assert.AreEqual("Alternative", ((string)null).WithAlternative("Alternative"));
+        }
     }
 }