Add a helper utility to clear the environment variables for tests (#115752)

This preserves most ambient variables other than LANG and anything prefixed with DOTNET_SYSTEM_GLOBALIZATION.

Fixes #100505

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Author: AndyAyersMS

src/libraries/Common/tests/TestUtilities/System/TestEnvironment.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections.Generic;
+
 namespace System
 {
     public static class TestEnvironment
@@ -17,5 +19,24 @@ public static bool IsStressModeEnabled
                 return value != null && (value == "1" || value.Equals("true", StringComparison.OrdinalIgnoreCase));
             }
         }
+
+        /// <summary>
+        /// Removes LANG and any environment variable starting with DOTNET_SYSTEM_GLOBALIZATION from the given environment dictionary.
+        /// </summary>
+        public static void ClearGlobalizationEnvironmentVars(IDictionary<string,string?> environment)
+        {
+            var keysToRemove = new List<string>();
+            foreach (var key in environment.Keys)
+            {
+                if (key == "LANG" || key.StartsWith("DOTNET_SYSTEM_GLOBALIZATION", StringComparison.OrdinalIgnoreCase))
+                {
+                    keysToRemove.Add(key);
+                }
+            }
+            foreach (var key in keysToRemove)
+            {
+                environment.Remove(key);
+            }
+        }
     }
 }

src/libraries/System.Memory/tests/Span/StringSearchValues.cs

@@ -597,7 +597,7 @@ private static void RunUsingInvariantCulture(Action action)
             Assert.True(CanTestInvariantCulture);
 
             var psi = new ProcessStartInfo();
-            psi.Environment.Clear();
+            TestEnvironment.ClearGlobalizationEnvironmentVars(psi.Environment);
             psi.Environment.Add("DOTNET_SYSTEM_GLOBALIZATION_INVARIANT", "true");
 
             RemoteExecutor.Invoke(action, new RemoteInvokeOptions { StartInfo = psi, TimeOut = 10 * 60 * 1000 }).Dispose();
@@ -608,7 +608,7 @@ private static void RunUsingNLS(Action action)
             Assert.True(CanTestNls);
 
             var psi = new ProcessStartInfo();
-            psi.Environment.Clear();
+            TestEnvironment.ClearGlobalizationEnvironmentVars(psi.Environment);
             psi.Environment.Add("DOTNET_SYSTEM_GLOBALIZATION_USENLS", "true");
 
             RemoteExecutor.Invoke(action, new RemoteInvokeOptions { StartInfo = psi, TimeOut = 10 * 60 * 1000 }).Dispose();

src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoCurrentCulture.cs

@@ -130,9 +130,7 @@ public void CurrentUICulture_Set_Null_ThrowsArgumentNullException()
         public void CurrentCulture_BasedOnLangEnvVar(string langEnvVar, string expectedCultureName)
         {
             var psi = new ProcessStartInfo();
-            psi.Environment.Clear();
-
-            CopyEssentialTestEnvironment(psi.Environment);
+            TestEnvironment.ClearGlobalizationEnvironmentVars(psi.Environment);
 
             psi.Environment["LANG"] = langEnvVar;
 
@@ -154,9 +152,7 @@ public void CurrentCulture_BasedOnLangEnvVar(string langEnvVar, string expectedC
         public void CurrentCulture_DefaultWithNoLang(string langEnvVar)
         {
             var psi = new ProcessStartInfo();
-            psi.Environment.Clear();
-
-            CopyEssentialTestEnvironment(psi.Environment);
+            TestEnvironment.ClearGlobalizationEnvironmentVars(psi.Environment);
 
             if (langEnvVar != null)
             {
@@ -187,20 +183,5 @@ public void CurrentCulture_DefaultWithNoLang(string langEnvVar)
                 }
             }, new RemoteInvokeOptions { StartInfo = psi }).Dispose();
         }
-
-        private static void CopyEssentialTestEnvironment(IDictionary<string, string> environment)
-        {
-            string[] essentialVariables = { "HOME", "LD_LIBRARY_PATH", "ICU_DATA" };
-            string[] prefixedVariables = { "DOTNET_", "COMPlus_", "SuperPMIShim" };
-
-            foreach (DictionaryEntry de in Environment.GetEnvironmentVariables())
-            {
-                if (Array.FindIndex(essentialVariables, x => x.Equals(de.Key)) >= 0 ||
-                    Array.FindIndex(prefixedVariables, x => ((string)de.Key).StartsWith(x, StringComparison.OrdinalIgnoreCase)) >= 0)
-                {
-                    environment[(string)de.Key] = (string)de.Value;
-                }
-            }
-        }
     }
 }

src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/GetCultureInfo.cs

@@ -147,7 +147,7 @@ public void TestFakeCultureNames(string name)
         public void PredefinedCulturesOnlyEnvVarTest(string predefinedCulturesOnlyEnvVar, string cultureName)
         {
             var psi = new ProcessStartInfo();
-            psi.Environment.Clear();
+            TestEnvironment.ClearGlobalizationEnvironmentVars(psi.Environment);
 
             psi.Environment.Add("DOTNET_SYSTEM_GLOBALIZATION_PREDEFINED_CULTURES_ONLY", predefinedCulturesOnlyEnvVar);
 
@@ -176,7 +176,7 @@ public void PredefinedCulturesOnlyEnvVarTest(string predefinedCulturesOnlyEnvVar
         public void TestAllowInvariantCultureOnly(bool enableInvariant, bool predefinedCulturesOnly, bool declarePredefinedCulturesOnly)
         {
             var psi = new ProcessStartInfo();
-            psi.Environment.Clear();
+            TestEnvironment.ClearGlobalizationEnvironmentVars(psi.Environment);
 
             if (enableInvariant)
             {