Add Utc test to ensure creating only one instance (dotnet/corefx#37721)

* Add Utc test to ensure creating only one instance

* Address the feedback

Commit migrated from https://github.com/dotnet/corefx/commit/39c7df85afee9ddc8bc1a1726a92526d43b1959f

diff --git a/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs b/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
index 9457cf1..8dc6f65 100644 (file)
--- a/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Linq;
 using System.Text.RegularExpressions;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
@@ -136,7 +137,7 @@ namespace System.Tests
 
         [Fact]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "The full .NET Framework has a bug. See https://github.com/dotnet/corefx/issues/26479")]
-        public static void CaseInsensiveLookup()
+        public static void CaseInsensitiveLookup()
         {
             Assert.Equal(TimeZoneInfo.FindSystemTimeZoneById(s_strBrasilia), TimeZoneInfo.FindSystemTimeZoneById(s_strBrasilia.ToLowerInvariant()));
             Assert.Equal(TimeZoneInfo.FindSystemTimeZoneById(s_strJohannesburg), TimeZoneInfo.FindSystemTimeZoneById(s_strJohannesburg.ToUpperInvariant()));
@@ -2243,6 +2244,15 @@ namespace System.Tests
             }
         }
 
+        [Fact]
+        [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
+        public static void EnsureUtcObjectSingleton()
+        {
+            TimeZoneInfo utcObject = TimeZoneInfo.GetSystemTimeZones().Single(x => x.Id.Equals("UTC", StringComparison.OrdinalIgnoreCase));
+            Assert.True(ReferenceEquals(utcObject, TimeZoneInfo.Utc));
+            Assert.True(ReferenceEquals(TimeZoneInfo.FindSystemTimeZoneById("UTC"), TimeZoneInfo.Utc));
+        }
+
         private static void VerifyConvertException<TException>(DateTimeOffset inputTime, string destinationTimeZoneId) where TException : Exception
         {
             Assert.ThrowsAny<TException>(() => TimeZoneInfo.ConvertTime(inputTime, TimeZoneInfo.FindSystemTimeZoneById(destinationTimeZoneId)));