Fixing System.Diagnostics.Tests.ProcessTests failures on Unix (#27670)

* Fixing System.Diagnostics.Tests.ProcessTests failures on Unix

Making sure we throw InvalidOperationException and with proper message to be consistent with netfx.
This fixes test HandleCountChanges and updates two other existing tests

Making s_allowedProgramsToRun field static in order to fix the 'field marshalling' error occuring during RemoteInvoke

Fixes #27459

* Changing back to existing exception type and correcting the test method accordingly

Author: maryamariyan

src/System.Diagnostics.Process/tests/ProcessTests.Unix.cs

@@ -592,6 +592,6 @@ private void RunTestAsSudo(Func<string, int> testMethod, string arg)
         [DllImport("libc")]
         private static extern int seteuid(uint euid);
 
-        private readonly string[] s_allowedProgramsToRun = new string[] { "xdg-open", "gnome-open", "kfmclient" };
+        private static readonly string[] s_allowedProgramsToRun = new string[] { "xdg-open", "gnome-open", "kfmclient" };
     }
 }

src/System.Diagnostics.Process/tests/ProcessTests.cs

@@ -923,10 +923,10 @@ public void GetProcesses_EmptyMachineName_ThrowsArgumentException()
 
         [Fact]
         [ActiveIssue(26720, TargetFrameworkMonikers.Uap)]
-        [ActiveIssue(27459)]
         public void GetProcesses_InvalidMachineName_ThrowsInvalidOperationException()
         {
-            Assert.Throws<InvalidOperationException>(() => Process.GetProcesses(Guid.NewGuid().ToString()));
+            Type exceptionType = PlatformDetection.IsWindows ? typeof(InvalidOperationException) : typeof(PlatformNotSupportedException);
+            var exception = Assert.Throws(exceptionType, () => Process.GetProcesses(Guid.NewGuid().ToString()));
         }
 
         [Fact]
@@ -1285,7 +1285,6 @@ public void TestHandleCount_OSX()
         [PlatformSpecific(TestPlatforms.Linux | TestPlatforms.Windows)]  // Expected process HandleCounts differs on OSX
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "Handle count change is not reliable, but seems less robust on NETFX")]
         [SkipOnTargetFramework(TargetFrameworkMonikers.Uap, "Retrieving information about local processes is not supported on uap")]
-        [ActiveIssue(27459)]
         public void HandleCountChanges()
         {
             RemoteInvoke(() =>