Increase decompiler test-suite CPU utilization via NUnit parallelism

ICSharpCode.Decompiler.Tests/CorrectnessTestRunner.cs

@@ -28,7 +28,9 @@
 
 namespace ICSharpCode.Decompiler.Tests
 {
-	[TestFixture, Parallelizable(ParallelScope.All)]
+	// Order(2) enqueues these long compile+execute tests right after the roundtrip fixture,
+	// ahead of unordered fixtures, so they do not straggle at the end of a parallel run.
+	[TestFixture, Parallelizable(ParallelScope.All), Order(2)]
 	public class CorrectnessTestRunner
 	{
 		static readonly string TestCasePath = Tester.TestCasePath + "/Correctness";

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -58,6 +58,17 @@
     <DefineConstants>TRACE;$(DefineConstants)</DefineConstants>
   </PropertyGroup>
 
+  <ItemGroup>
+    <!-- NUnit's default worker count (one per logical CPU) underutilizes the machine because
+         most matrix tests block on child processes (csc/vbc/ilasm/msbuild/test runners).
+         LevelOfParallelism only accepts a constant, so compute 2x logical CPUs at build time;
+         the machine building the tests is the machine running them. -->
+    <AssemblyAttribute Include="NUnit.Framework.LevelOfParallelism">
+      <_Parameter1>$([MSBuild]::Multiply($([System.Environment]::ProcessorCount), 2))</_Parameter1>
+      <_Parameter1_TypeName>System.Int32</_Parameter1_TypeName>
+    </AssemblyAttribute>
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="DiffLib" />
     <PackageReference Include="CliWrap" />

ICSharpCode.Decompiler.Tests/Properties/AssemblyInfo.cs

@@ -22,8 +22,15 @@
 using System.Reflection;
 using System.Runtime.InteropServices;
 
+using NUnit.Framework;
+
 #endregion
 
+// Fixtures without their own Parallelizable attribute run concurrently with other fixtures;
+// tests within such a fixture still run sequentially. Fixtures that share process-global
+// state must opt out individually with [NonParallelizable].
+[assembly: Parallelizable(ParallelScope.Fixtures)]
+
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]
 

ICSharpCode.Decompiler.Tests/RoundtripAssembly.cs

@@ -36,7 +36,9 @@
 
 namespace ICSharpCode.Decompiler.Roundtrip
 {
-	[TestFixture, Parallelizable(ParallelScope.All), Platform("Win")]
+	// Order(1) enqueues this fixture's multi-minute roundtrip tests ahead of unordered
+	// fixtures, so they do not straggle at the end of a parallel run.
+	[TestFixture, Parallelizable(ParallelScope.All), Platform("Win"), Order(1)]
 	public class RoundtripAssembly
 	{
 		public static readonly string TestDir = Path.GetFullPath(Path.Combine(Tester.TestCasePath, "../../ILSpy-tests"));

doc/WindowsDefenderExclusions.md

@@ -0,0 +1,60 @@
+# Windows Defender exclusions for test runs
+
+Real-time protection scans every file the test suite writes and every process it
+spawns. A full `ICSharpCode.Decompiler.Tests` run compiles thousands of fixture
+assemblies and launches csc/vbc/ilasm/msbuild/test-runner child processes; while it
+runs, `MsMpEng.exe` (Defender's scan engine) has been measured using 1-4 CPU cores
+continuously, and each process start pays additional scan latency. Excluding the
+folders below removes that overhead.
+
+**Security tradeoff:** excluded folders are not scanned at all. Only add exclusions
+on a development machine you control, and only for paths that contain code you
+build yourself. If you use a third-party antivirus or backup suite with real-time
+scanning (e.g. Acronis Active Protection), configure equivalent exclusions there.
+
+## Folders to exclude
+
+1. **The ILSpy repository clone** (e.g. `C:\src\ILSpy`). This covers everything the
+   build and tests write inside the repo:
+   - `bin\` and `obj\` of every project
+   - compiled test fixtures placed next to their sources under
+     `ICSharpCode.Decompiler.Tests\TestCases\`
+   - the Roslyn toolsets, reference-assembly packs, and vswhere that
+     `Tester.Initialize()` downloads under the test output directory
+   - the `ILSpy-tests\` submodule, including the `*-decompiled` / `*-output`
+     folders the roundtrip tests generate next to their inputs
+2. **The test-assembly temp path, if you redirected it.** When
+   `ICSharpCode.Decompiler.Tests\DecompilerTests.config.json` sets
+   `TestsAssemblyTempPath`, compiled fixtures land there instead of inside the
+   repo - exclude that folder as well.
+3. **Optional: the NuGet package cache** (`%USERPROFILE%\.nuget\packages`). Only
+   restore performance benefits; packages are signed and hash-verified by NuGet,
+   but skip this one if you prefer scanned downloads.
+
+The user temp folder (`%TEMP%`) also receives small diff files from failing
+correctness tests, but excluding all of `%TEMP%` is a poor tradeoff - malware
+routinely stages there. Leave it scanned.
+
+## Adding the exclusions
+
+Run PowerShell **as Administrator**, adjusting the paths to your clone:
+
+```powershell
+Add-MpPreference -ExclusionPath "C:\src\ILSpy"
+# only if TestsAssemblyTempPath is configured:
+Add-MpPreference -ExclusionPath "D:\ILSpyTestAssemblies"
+# optional:
+Add-MpPreference -ExclusionPath "$env:USERPROFILE\.nuget\packages"
+```
+
+## Verifying
+
+```powershell
+Get-MpPreference | Select-Object -ExpandProperty ExclusionPath
+```
+
+## Removing
+
+```powershell
+Remove-MpPreference -ExclusionPath "C:\src\ILSpy"
+```