implement test for Long Paths support in ProcessModule.FileName (#46685)

src/libraries/System.Diagnostics.Process/System.Diagnostics.Process.sln

 Microsoft Visual Studio Solution File, Format Version 12.00
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TestUtilities", "..\Common\tests\TestUtilities\TestUtilities.csproj", "{3742D5F8-5C86-49FD-BAEA-050742CCEB7A}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "LongPath", "tests\LongPath\LongPath.csproj", "{C67553AE-F09B-407D-AD3E-D61950E06BE8}"
+EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Win32.Registry", "..\Microsoft.Win32.Registry\ref\Microsoft.Win32.Registry.csproj", "{AA583AE2-BE26-4AA4-845F-916133916B7D}"
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Win32.Registry", "..\Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj", "{E5AE4EB3-DB23-4F33-858B-63B68A60F7F1}"
@@ -50,6 +52,7 @@ EndProject
 Global
 	GlobalSection(NestedProjects) = preSolution
 		{3742D5F8-5C86-49FD-BAEA-050742CCEB7A} = {05C87914-711A-4589-9672-8169DB6A6BA4}
+		{C67553AE-F09B-407D-AD3E-D61950E06BE8} = {05C87914-711A-4589-9672-8169DB6A6BA4}
 		{ABA61FEF-EB06-441D-9D3D-F25FFC7CD83D} = {05C87914-711A-4589-9672-8169DB6A6BA4}
 		{AA583AE2-BE26-4AA4-845F-916133916B7D} = {9ABDFB23-5430-4410-81C3-3C0327996580}
 		{4792FFA1-1AD2-4230-8DE3-D2BCF1CF804F} = {9ABDFB23-5430-4410-81C3-3C0327996580}
@@ -160,6 +163,10 @@ Global
 		{9C521ED1-5221-4C93-BBA0-86C13D4C23C7}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{9C521ED1-5221-4C93-BBA0-86C13D4C23C7}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{9C521ED1-5221-4C93-BBA0-86C13D4C23C7}.Release|Any CPU.Build.0 = Release|Any CPU
+		{C67553AE-F09B-407D-AD3E-D61950E06BE8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C67553AE-F09B-407D-AD3E-D61950E06BE8}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C67553AE-F09B-407D-AD3E-D61950E06BE8}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{C67553AE-F09B-407D-AD3E-D61950E06BE8}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/libraries/System.Diagnostics.Process/tests/LongPath/ClassDefinedInAssemblyWithAVeryLongPath.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System
+{
+    // this type is not used anywhere, but it exists so the containing `.dll` is not empty and
+    // can be copied to the output folder and be dynamically loaded during test execution
+    public class ClassDefinedInAssemblyWithAVeryLongPath
+    {
+    }
+}

src/libraries/System.Diagnostics.Process/tests/LongPath/LongPath.csproj

+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="ClassDefinedInAssemblyWithAVeryLongPath.cs" />
+  </ItemGroup>
+</Project>

src/libraries/System.Diagnostics.Process/tests/ProcessModuleTests.cs

 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.IO;
 using System.Linq;
+using System.Reflection;
 using Microsoft.DotNet.RemoteExecutor;
 using Xunit;
 
@@ -89,5 +91,33 @@ public void ModulesAreDisposedWhenProcessIsDisposed()
             process.Dispose();
             Assert.Equal(expectedCount, disposedCount);
         }
+
+        [ActiveIssue("https://github.com/dotnet/runtime/pull/335059")]
+        [ConditionalFact(typeof(PathFeatures), nameof(PathFeatures.AreAllLongPathsAvailable))]
+        [PlatformSpecific(TestPlatforms.Windows)]
+        public void LongModuleFileNamesAreSupported()
+        {
+            // To be able to test Long Path support for ProcessModule.FileName we need a .dll that has a path >= 260 chars.
+            // Since Long Paths support can be disabled (see the ConditionalFact attribute usage above),
+            // we just copy "LongName.dll" from bin to a temp directory with a long name and load it from there.
+            // Loading from new path is possible because the type exposed by the assembly is not referenced in any explicit way.
+            const string libraryName = "LongPath.dll";
+
+            string testBinPath = Path.GetDirectoryName(typeof(ProcessModuleTests).Assembly.Location);
+            string libraryToCopy = Path.Combine(testBinPath, libraryName);
+            Assert.True(File.Exists(libraryToCopy), $"{libraryName} was not present in bin folder '{testBinPath}'");
+
+            string directoryWithLongName = Path.Combine(TestDirectory, new string('a', Math.Max(1, 261 - TestDirectory.Length)));
+            Directory.CreateDirectory(directoryWithLongName);
+
+            string longNamePath = Path.Combine(directoryWithLongName, libraryName);
+            Assert.True(longNamePath.Length > 260);
+
+            File.Copy(libraryToCopy, longNamePath);
+
+            Assembly loaded = Assembly.LoadFile(longNamePath);
+
+            Assert.Contains(Process.GetCurrentProcess().Modules.Cast<ProcessModule>(), module => module.FileName == longNamePath);
+        }
     }
 }

src/libraries/System.Diagnostics.Process/tests/System.Diagnostics.Process.Tests.csproj

@@ -17,6 +17,8 @@
              Link="Common\Microsoft\Win32\TempRegistryKey.cs" />
     <Compile Include="$(CommonPath)System\Text\ValueStringBuilder.cs"
              Link="Common\System\Text\ValueStringBuilder.cs" />
+    <Compile Include="$(CommonTestPath)System\IO\PathFeatures.cs"
+             Link="Common\System\IO\PathFeatures.cs" />
     <Compile Include="DelegateSynchronizeInvoke.cs" />
     <Compile Include="FileAssociations.cs" />
     <Compile Include="Helpers.cs" />
@@ -50,5 +52,6 @@
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+    <ProjectReference Include="LongPath\LongPath.csproj" />
   </ItemGroup>
 </Project>