diff --git a/X10D.Tests/src/Core/CharTests.cs b/X10D.Tests/src/Core/CharTests.cs
index 1f4efe7..e973ceb 100644
--- a/X10D.Tests/src/Core/CharTests.cs
+++ b/X10D.Tests/src/Core/CharTests.cs
@@ -1,4 +1,4 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace X10D.Tests.Core
 {
@@ -8,26 +8,17 @@ namespace X10D.Tests.Core
     [TestClass]
     public class CharTests
     {
-        /// <summary>
-        ///     Tests for <see cref="CharExtensions.Repeat" />.
-        /// </summary>
-        [TestMethod]
-        public void Random()
-        {
-            var set = "abcdefghijklmnopqrstuvwxyz".ToCharArray();
-            var random = set.Random(20);
-
-            Assert.IsTrue(random.All(c => Array.IndexOf(set, c) >= 0));
-            Assert.IsFalse(random.Any(c => Array.IndexOf(set, c) < -1));
-        }
-
-        /// <summary>
-        ///     Tests for <see cref="CharExtensions.Repeat" />.
-        /// </summary>
         [TestMethod]
         public void Repeat()
         {
-            Assert.AreEqual("aaaaaaaaaa", 'a'.Repeat(10));
+            const char character = 'a';
+            const int repeatCount = 10;
+
+            const string repeated = "aaaaaaaaaa";
+            var result = character.Repeat(repeatCount);
+
+            Assert.AreEqual(repeated, result);
+            Assert.ThrowsException<ArgumentOutOfRangeException>(() => character.Repeat(-1));
         }
     }
 }