Fix MTP timeout parsing to use invariant culture instead of current culture

src/Platform/Microsoft.Testing.Platform/CommandLine/PlatformCommandLineProvider.cs

@@ -111,7 +111,7 @@ public Task<ValidationResult> ValidateOptionArgumentsAsync(CommandLineOption com
         {
             string arg = arguments[0];
             int size = arg.Length;
-            if ((char.ToLowerInvariant(arg[size - 1]) != 'h' && char.ToLowerInvariant(arg[size - 1]) != 'm' && char.ToLowerInvariant(arg[size - 1]) != 's') || !float.TryParse(arg[..(size - 1)], out float _))
+            if ((char.ToLowerInvariant(arg[size - 1]) != 'h' && char.ToLowerInvariant(arg[size - 1]) != 'm' && char.ToLowerInvariant(arg[size - 1]) != 's') || !float.TryParse(arg[..(size - 1)], NumberStyles.Float, CultureInfo.InvariantCulture, out float _))
             {
                 return ValidationResult.InvalidTask(PlatformResources.PlatformCommandLineTimeoutArgumentErrorMessage);
             }

src/Platform/Microsoft.Testing.Platform/Hosts/TestHostBuilder.cs

@@ -255,7 +255,7 @@ public async Task<ITestHost> BuildAsync(
         {
             string arg = args[0];
             int size = arg.Length;
-            if (!float.TryParse(arg[..(size - 1)], out float value))
+            if (!float.TryParse(arg[..(size - 1)], NumberStyles.Float, CultureInfo.InvariantCulture, out float value))
             {
                 throw ApplicationStateGuard.Unreachable();
             }

test/UnitTests/Microsoft.Testing.Platform.UnitTests/CommandLine/PlatformCommandLineProviderTests.cs

@@ -181,4 +181,82 @@
         Assert.IsFalse(validateOptionsResult.IsValid);
         Assert.IsTrue(validateOptionsResult.ErrorMessage.StartsWith($"Invalid PID '{pid}'", StringComparison.OrdinalIgnoreCase));
     }
+
+    [TestMethod]
+    [DataRow("1.5s")]
+    [DataRow("2.0m")]
+    [DataRow("0.5h")]
+    [DataRow("10s")]
+    [DataRow("30m")]
+    [DataRow("1h")]
+    public async Task IsValid_If_Timeout_Has_CorrectFormat_InvariantCulture(string timeout)
+    {
+        var provider = new PlatformCommandLineProvider();
+        CommandLineOption option = provider.GetCommandLineOptions().First(x => x.Name == PlatformCommandLineProvider.TimeoutOptionKey);
+
+        // Save current culture
+        CultureInfo originalCulture = CultureInfo.CurrentCulture;
+
+        try
+        {
+            // Test with various cultures to ensure invariant parsing works
+            foreach (string cultureName in new[] { "en-US", "de-DE", "fr-FR" })
+            {
+                CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo(cultureName);
+
+                ValidationResult validateOptionsResult = await provider.ValidateOptionArgumentsAsync(option, [timeout]).ConfigureAwait(false);
+                Assert.IsTrue(validateOptionsResult.IsValid, $"Failed with culture {cultureName} and timeout {timeout}");
+                Assert.IsTrue(string.IsNullOrEmpty(validateOptionsResult.ErrorMessage));
+            }
+        }
+        finally
+        {
+            // Restore original culture
+            CultureInfo.CurrentCulture = originalCulture;
+        }
+    }
+
+    [TestMethod]
+    [DataRow("1,5s")] // German decimal separator
+    [DataRow("invalid")]
+    [DataRow("1.5")]  // Missing unit
+    [DataRow("abc.5s")]
+    public async Task IsInvalid_If_Timeout_Has_IncorrectFormat(string timeout)
+    {
+        var provider = new PlatformCommandLineProvider();
+        CommandLineOption option = provider.GetCommandLineOptions().First(x => x.Name == PlatformCommandLineProvider.TimeoutOptionKey);
+
+        ValidationResult validateOptionsResult = await provider.ValidateOptionArgumentsAsync(option, [timeout]).ConfigureAwait(false);
+        Assert.IsFalse(validateOptionsResult.IsValid);
+        Assert.AreEqual(PlatformResources.PlatformCommandLineTimeoutArgumentErrorMessage, validateOptionsResult.ErrorMessage);
+    }
+
+    [TestMethod]
+    public async Task Timeout_Parsing_Uses_InvariantCulture_NotCurrentCulture()
+    {
+        var provider = new PlatformCommandLineProvider();
+        CommandLineOption option = provider.GetCommandLineOptions().First(x => x.Name == PlatformCommandLineProvider.TimeoutOptionKey);
+
+        // Save current culture
+        CultureInfo originalCulture = CultureInfo.CurrentCulture;
+
+        try
+        {
+            // Set culture to German where decimal separator is comma
+            CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("de-DE");
+
+            // This should work because we use invariant culture (period as decimal separator)
+            ValidationResult validResult = await provider.ValidateOptionArgumentsAsync(option, ["1.5s"]).ConfigureAwait(false);
+            Assert.IsTrue(validResult.IsValid, "1.5s should be valid when using invariant culture");
+
+            // This should fail because comma is not valid in invariant culture
+            ValidationResult invalidResult = await provider.ValidateOptionArgumentsAsync(option, ["1,5s"]).ConfigureAwait(false);
+            Assert.IsFalse(invalidResult.IsValid, "1,5s should be invalid when using invariant culture");
+        }
+        finally
+        {
+            // Restore original culture
+            CultureInfo.CurrentCulture = originalCulture;
+        }
+    }
 }