test: fix timezone tests to work with different TZ IDs on windows and linux, and fix mocker behavior on .NET 4.x

Author: anthonyreilly

src/NetCoreForce.Client.Tests/TimeZoneIds.cs

@@ -1,16 +1,29 @@
 using System;
-using System.Reflection;
+using System.Collections.Generic;
 
 namespace NetCoreForce.Client.Tests
-{   
+{
     /// <summary>
-    /// Sample TimeZone IDs for use in tests
+    /// Sample TimeZone IDs for use in tests.
+    /// Windows and Linux/macOS use different TimeZoneInfo ID formats (Windows-native vs IANA),
+    /// so the appropriate ID for the current OS is exposed here.
     /// </summary>
     public static class TimeZoneIds
     {
-        public static string TimeZoneIdNewYork = "America/New_York";
-        public static string TimeZoneIdPhoenix = "America/Phoenix";
-        public static string TimeZoneIdLondon = "Europe/London";
-        public static string TimeZoneIdTokyo = "Asia/Tokyo";
+        private static readonly bool IsWindows = Environment.OSVersion.Platform == PlatformID.Win32NT;
+
+        public static string NewYork => IsWindows ? "Eastern Standard Time" : "America/New_York";
+        public static string Phoenix => IsWindows ? "US Mountain Standard Time" : "America/Phoenix"; // no DST
+        public static string London => IsWindows ? "GMT Standard Time" : "Europe/London";
+        public static string Tokyo => IsWindows ? "Tokyo Standard Time" : "Asia/Tokyo";
+        public static string Kathmandu => IsWindows ? "Nepal Standard Time" : "Asia/Kathmandu"; // UTC+5:45
+        public static string Auckland => IsWindows ? "New Zealand Standard Time" : "Pacific/Auckland";
+        public static string Moscow => IsWindows ? "Russian Standard Time" : "Europe/Moscow";
+        public static string Shanghai => IsWindows ? "China Standard Time" : "Asia/Shanghai";
+
+        public static IEnumerable<string> All => new[]
+        {
+            NewYork, Phoenix, London, Tokyo, Kathmandu, Auckland, Moscow, Shanghai
+        };
     }
 }

src/NetCoreForce.Client.Tests/TimeZoneInfoMocker.cs

@@ -13,12 +13,24 @@ public LocalTimeZoneInfoMocker(TimeZoneInfo mockTimeZoneInfo)
             SetLocalTimeZone(mockTimeZoneInfo);
         }
 
+        // the private field backing TimeZoneInfo.Local is named "_localTimeZone" on modern .NET,
+        // but "m_localTimeZone" on .NET Framework
+        private static readonly string[] LocalTimeZoneFieldNames = { "_localTimeZone", "m_localTimeZone" };
+
         private static void SetLocalTimeZone(TimeZoneInfo timeZoneInfo)
         {
             var info = typeof(TimeZoneInfo).GetField("s_cachedData", BindingFlags.NonPublic | BindingFlags.Static);
             object cachedData = info.GetValue(null);
 
-            var field = cachedData.GetType().GetField("_localTimeZone", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Instance);
+            FieldInfo field = null;
+            foreach (string fieldName in LocalTimeZoneFieldNames)
+            {
+                field = cachedData.GetType().GetField(fieldName, BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static);
+                if (field != null) break;
+            }
+
+            if (field == null) throw new InvalidOperationException("Unable to find the local time zone field on TimeZoneInfo.CachedData");
+
             field.SetValue(cachedData, timeZoneInfo);
         }
 

src/NetCoreForce.Client.Tests/TimeZoneInfoMockerTests.cs

@@ -10,15 +10,10 @@ namespace NetCoreForce.Client.Tests
 {
     public class TimeZoneInfoMockerTests
     {
+        public static TheoryData<string> TimeZoneIdData => new TheoryData<string>(TimeZoneIds.All);
+
         [Theory]
-        [InlineData("America/New_York")]
-        [InlineData("America/Phoenix")]
-        [InlineData("Europe/London")]
-        [InlineData("Asia/Tokyo")]
-        [InlineData("Asia/Kathmandu")] // Nepal Time (UTC+5:45)
-        [InlineData("Pacific/Auckland")]
-        [InlineData("Europe/Moscow")]
-        [InlineData("Asia/Shanghai")]
+        [MemberData(nameof(TimeZoneIdData))]
         public void TestLocalTimeZoneInfoMocker(string timeZoneId)
         {
             TimeZoneInfo localTimeZoneInfo = TimeZoneInfo.Local;