PosixSignalRegistrationTests.Unix: validate signal pal mapping (#58711)

* PosixSignalRegistrationTests.Unix: validate signal pal mapping

* Use InvariantCulture for pid ToString

* Invoke kill through shell.

* Remove InvariantCulture

Author: tmds

src/libraries/System.Runtime.InteropServices/tests/System/Runtime/InteropServices/PosixSignalRegistrationTests.Unix.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Xunit;
+using System.Diagnostics;
+using System.Globalization;
 using System.Threading;
 using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
@@ -57,7 +59,16 @@ public void SignalHandlerCalledForKnownSignals(PosixSignal s)
                     semaphore.Release();
                 });
 
-                kill(signal);
+                // Use 'kill' command with signal name to validate the signal pal mapping.
+                string sigArg = signalStr.StartsWith("SIG") ? signalStr.Substring(3) : signalStr;
+                using var process = Process.Start(new ProcessStartInfo
+                    {
+                        FileName = "/bin/sh", // Use a shell because not all platforms include a 'kill' executable.
+                        ArgumentList = { "-c", $"kill -s {sigArg} {Environment.ProcessId.ToString()}" }
+                    });
+                process.WaitForExit();
+                Assert.Equal(0, process.ExitCode);
+
                 bool entered = semaphore.Wait(SuccessTimeout);
                 Assert.True(entered);
             }, s.ToString()).Dispose();