Added Missing unit tests for chapters 20 and 21

src/Chapter20.Tests/Listing20.07.Tests.cs

@@ -0,0 +1,15 @@
+//using Microsoft.VisualStudio.TestTools.UnitTesting;
+//using System.Threading.Tasks;
+
+//namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter20.Listing20_07.Tests
+//{
+//    [TestClass]
+//    public class ProgramTests
+//    {
+//        [TestMethod]
+//        public async Task MainTest()
+//        {
+//            await IntelliTect.TestTools.Console.ConsoleAssert.ExpectAsync("<filename>", async () => await AsyncEncryptionCollection.Main());
+//        }
+//    }
+//}

src/Chapter20/Listing20.07.AsynchronousStreamsInvocationWithAwaitForeach.cs

@@ -16,7 +16,7 @@ public async IAsyncEnumerator<string> GetAsyncEnumerator(
             #endregion EXCLUDE
         }
 
-        public static async void Main()
+        public static async Task Main()
         {
             AsyncEncryptionCollection collection =
                 new AsyncEncryptionCollection();

src/Chapter21.Tests/Listing21.01.Tests.cs

@@ -0,0 +1,17 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter21.Listing21_01.Tests
+{
+    [TestClass]
+    public class ProgramTests
+    {
+        [TestMethod]
+        public void MainTest()
+        {
+            const string expected = @"3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679";
+
+            IntelliTect.TestTools.Console.ConsoleAssert.Expect(
+                expected, Program.Main);
+        }
+    }
+}

src/Chapter21.Tests/Listing21.02.Tests.cs

@@ -0,0 +1,17 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter21.Listing21_02.Tests
+{
+    [TestClass]
+    public class ProgramTests
+    {
+        [TestMethod]
+        public void MainTest()
+        {
+            const string expected = @"3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679";
+
+            IntelliTect.TestTools.Console.ConsoleAssert.Expect(
+                expected, Program.Main);
+        }
+    }
+}

src/Chapter21.Tests/Listing21.04.Tests.cs

@@ -0,0 +1,18 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter21.Listing21_04.Tests
+{
+    [TestClass]
+    public class ProgramTests
+    {
+        [TestMethod]
+        public void MainTest()
+        {
+            const string expected = @"ERROR: AggregateException:
+  UnauthorizedAccessException - Attempted to perform an unauthorized operation.*";
+
+            IntelliTect.TestTools.Console.ConsoleAssert.ExpectLike(
+                expected, Program.Main);
+        }
+    }
+}