chore: Introduce a CultureSwitcher to make culture-based testing simpler

Src/Support/Google.Apis.Tests/Apis/Utils/UtilitiesTest.cs

@@ -129,19 +129,11 @@ public void GetStringFromDateTimeOffset_MillisecondHandling(int tickOfSecond, st
         [Fact]
         public void DateTimeOffsetConversionsAreInvariant()
         {
-            var originalCulture = Thread.CurrentThread.CurrentCulture;
-            try
-            {
-                Thread.CurrentThread.CurrentCulture = new CultureInfo("da-DK");
-                var dto = new DateTimeOffset(2023, 6, 13, 15, 54, 13, 500, TimeSpan.Zero);
-                string text = "2023-06-13T15:54:13.500Z";
-                Assert.Equal(text, Utilities.GetStringFromDateTimeOffset(dto));
-                Assert.Equal(dto, Utilities.GetDateTimeOffsetFromString(text));
-            }
-            finally
-            {
-                Thread.CurrentThread.CurrentCulture = originalCulture;
-            }
+            using var _ = new CultureSwitcher("da-DK");
+            var dto = new DateTimeOffset(2023, 6, 13, 15, 54, 13, 500, TimeSpan.Zero);
+            string text = "2023-06-13T15:54:13.500Z";
+            Assert.Equal(text, Utilities.GetStringFromDateTimeOffset(dto));
+            Assert.Equal(dto, Utilities.GetDateTimeOffsetFromString(text));
         }
 
         // Local time of 2023-06-13T15:54:13, with variable UTC offset.

Src/Support/Google.Apis.Tests/CultureSwitcher.cs

@@ -0,0 +1,60 @@
+/*
+Copyright 2023 Google LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+using System;
+using System.Globalization;
+
+namespace Google.Apis.Tests;
+
+/// <summary>
+/// Disposable class to help test code in different cultures.
+/// On construction, this changes the current thread's current culture
+/// to the specified one (and remembers the original culture). On disposal,
+/// the original culture is restored.
+/// </summary>
+internal class CultureSwitcher : IDisposable
+{
+    private readonly CultureInfo _originalCulture;
+
+    /// <summary>
+    /// Creates a new instance based on the name of the culture to switch to.
+    /// </summary>
+    internal CultureSwitcher(string name) : this(new CultureInfo(name))
+    {
+    }
+
+    /// <summary>
+    /// Creates a new instance switching to the specified culture.
+    /// </summary>
+    internal CultureSwitcher(CultureInfo newCulture)
+    {
+        _originalCulture = CultureInfo.CurrentCulture;
+        SetCulture(newCulture);
+    }
+
+    public void Dispose() => SetCulture(_originalCulture);
+
+    private void SetCulture(CultureInfo culture)
+    {
+        // CultureInfo.CurrentCulture is the preferred way to set this,
+        // but it was read-only on .NET Framework before v4.6.
+#if NET452
+        System.Threading.Thread.CurrentThread.CurrentCulture = culture;
+#else
+        CultureInfo.CurrentCulture = culture;
+#endif
+    }
+}