Add test

Author: Copilot

test/TestAssets/TestProjects/ConsoleAppDoesNothing/ConsoleAppDoesNothing.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), testAsset.props))\testAsset.props" />
+
+	<PropertyGroup>
+		<TargetFramework>$(CurrentTargetFramework)</TargetFramework>
+		<OutputType>Exe</OutputType>
+		<ManagePackageVersionsCentrally>false</ManagePackageVersionsCentrally>
+		<IsTestingPlatformApplication>true</IsTestingPlatformApplication>
+	</PropertyGroup>
+
+</Project>

test/TestAssets/TestProjects/ConsoleAppDoesNothing/Program.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace ConsoleAppDoesNothing;
+
+public class Program
+{
+    /// <summary>
+    /// A console application that does "nothing" - just exits without any handshake or testing platform interaction.
+    /// This is used to test dotnet test behavior with non-MTP console applications.
+    /// </summary>
+    public static void Main(string[] args)
+    {
+        // Intentionally does nothing - no handshake, no test framework, just exits
+        // This simulates a regular console app that doesn't implement MTP protocol
+    }
+}

test/dotnet.Tests/CommandTests/Test/GivenDotnetTestRunsConsoleAppWithoutHandshake.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.DotNet.Cli.Commands.Test;
+using CommandResult = Microsoft.DotNet.Cli.Utils.CommandResult;
+using ExitCodes = Microsoft.NET.TestFramework.ExitCode;
+
+namespace Microsoft.DotNet.Cli.Test.Tests
+{
+    public class GivenDotnetTestRunsConsoleAppWithoutHandshake : SdkTest
+    {
+        public GivenDotnetTestRunsConsoleAppWithoutHandshake(ITestOutputHelper log) : base(log)
+        {
+        }
+
+        [InlineData(TestingConstants.Debug)]
+        [InlineData(TestingConstants.Release)]
+        [Theory]
+        public void RunConsoleAppDoesNothing_ShouldReturnCorrectExitCode(string configuration)
+        {
+            // This test validates the behavior when running `dotnet test` against a console application
+            // that does "nothing" and doesn't implement the MTP (Message Transport Protocol) handshake.
+            // 
+            // The issue (#49733) suggests that silently ignoring such applications is not good behavior.
+            // This test validates that the improved behavior provides a meaningful error message.
+
+            TestAsset testInstance = _testAssetsManager.CopyTestAsset("ConsoleAppDoesNothing", Guid.NewGuid().ToString())
+                .WithSource();
+
+            CommandResult result = new DotnetTestCommand(Log, disableNewOutput: false)
+                                    .WithWorkingDirectory(testInstance.Path)
+                                    .Execute(TestingPlatformOptions.ConfigurationOption.Name, configuration);
+
+            if (!TestContext.IsLocalized())
+            {
+                // The new behavior should provide a clear error message indicating that
+                // the console app is not a test project and doesn't implement MTP
+                result.StdOut.Should().Contain("is not a test project and does not implement the testing platform protocol");
+                result.StdOut.Should().Contain("ConsoleAppDoesNothing.csproj");
+            }
+
+            // The new behavior should return GenericFailure exit code instead of success
+            result.ExitCode.Should().Be(ExitCodes.GenericFailure, 
+                "dotnet test should fail with a meaningful error when run against console app without MTP handshake");
+        }
+    }
+}