forbid deep inheritance

NUnit.Analyzers/Constants/AnalyzerIdentifiers.cs

@@ -4,5 +4,6 @@ internal static class AnalyzerIdentifiers
     {
         internal const string TestFieldIsNotReadonly = "NU0001";
         internal const string TestUsesSetupAttributes = "NU0002";
+        internal const string TestDeepInheritanceChain = "NU0003";
     }
 }

NUnit.Analyzers/README.md

@@ -6,3 +6,4 @@
 Couple of nunit analyzers, helpful for parallel tests:
 - NU0001 Warning: TestFieldIsNotReadonly
 - NU0002 Warning: TestUsesSetupAttributes
+- NU0003 Warning: TestDeepInheritanceChain

NUnit.Analyzers/TestDeepInheritanceChain/TestDeepInheritanceChainAnalyzer.cs

@@ -0,0 +1,60 @@
+using System.Collections.Immutable;
+using System.Linq;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+using SkbKontur.NUnit.Analyzers.Constants;
+using SkbKontur.NUnit.Analyzers.Extensions;
+
+namespace SkbKontur.NUnit.Analyzers.TestDeepInheritanceChain
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public class TestDeepInheritanceChainAnalyzer : DiagnosticAnalyzer
+    {
+        public override void Initialize(AnalysisContext context)
+        {
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+            context.EnableConcurrentExecution();
+            context.RegisterSymbolAction(AnalyzeType, SymbolKind.NamedType);
+        }
+
+        private static void AnalyzeType(SymbolAnalysisContext context)
+        {
+            var typeSymbol = (INamedTypeSymbol)context.Symbol;
+
+            var hasTests = typeSymbol
+                           .GetMembers()
+                           .OfType<IMethodSymbol>()
+                           .Any(x => x.MethodKind == MethodKind.Ordinary && x.IsTestRelatedMethod(context.Compilation));
+
+            if (!hasTests)
+                return;
+
+            var testBase = typeSymbol.BaseType?.BaseType;
+            if (testBase != null && !knownRoots.Any(r => testBase.IsType(r, context.Compilation)))
+                context.ReportDiagnostic(Diagnostic.Create(testDeepInheritanceChain, typeSymbol.Locations[0]));
+        }
+
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics =>
+            ImmutableArray.Create(testDeepInheritanceChain);
+
+        private static readonly DiagnosticDescriptor testDeepInheritanceChain = new DiagnosticDescriptor(
+            AnalyzerIdentifiers.TestDeepInheritanceChain,
+            TestDeepInheritanceChainConstants.TestDeepInheritanceChainTitle,
+            TestDeepInheritanceChainConstants.TestDeepInheritanceChainMessage,
+            Categories.ParallelExecution,
+            DiagnosticSeverity.Warning,
+            true,
+            TestDeepInheritanceChainConstants.TestDeepInheritanceChainDescription,
+            TestDeepInheritanceChainConstants.TestDeepInheritanceChainUri
+        );
+
+        private static readonly string[] knownRoots =
+            {
+                "System.Object",
+                "SkbKontur.NUnit.Middlewares.SimpleTestBase",
+                "SkbKontur.NUnit.Middlewares.SimpleSuiteBase",
+            };
+    }
+}

NUnit.Analyzers/TestDeepInheritanceChain/TestDeepInheritanceChainConstants.cs

@@ -0,0 +1,10 @@
+namespace SkbKontur.NUnit.Analyzers.TestDeepInheritanceChain
+{
+    internal static class TestDeepInheritanceChainConstants
+    {
+        internal const string TestDeepInheritanceChainTitle = "Test base inheritance chain is too deep";
+        internal const string TestDeepInheritanceChainMessage = "Test base inheritance chain is too deep";
+        internal const string TestDeepInheritanceChainDescription = "Test fixture class should have only one base class for clarity.";
+        internal const string TestDeepInheritanceChainUri = "https://en.wikipedia.org/wiki/Composition_over_inheritance";
+    }
+}

README.md

@@ -2,10 +2,11 @@
 
 A collection of extensions for NUnit.
 
-|                                     | Build Status |
-|-------------------------------------|:--------------: |
-| NUnit.Middlewares | [![NuGet Status](https://img.shields.io/nuget/v/SkbKontur.NUnit.Middlewares.svg)](https://www.nuget.org/packages/SkbKontur.NUnit.Middlewares/) |
-| NUnit.Retries | [![NuGet Status](https://img.shields.io/nuget/v/SkbKontur.NUnit.Retries.svg)](https://www.nuget.org/packages/SkbKontur.NUnit.Retries/) |
+|                   | Build Status    |
+|-------------------|:--------------: |
+| NUnit.Analyzers   | [![NuGet Status](https://img.shields.io/nuget/v/SkbKontur.NUnit.Analyzers.svg)](https://www.nuget.org/packages/SkbKontur.NUnit.Analyzers/)                      |
+| NUnit.Middlewares | [![NuGet Status](https://img.shields.io/nuget/v/SkbKontur.NUnit.Middlewares.svg)](https://www.nuget.org/packages/SkbKontur.NUnit.Middlewares/)                  |
+| NUnit.Retries     | [![NuGet Status](https://img.shields.io/nuget/v/SkbKontur.NUnit.Retries.svg)](https://www.nuget.org/packages/SkbKontur.NUnit.Retries/)                          |
 | Build             | [![Build status](https://github.com/skbkontur/nunit-extensions/actions/workflows/actions.yml/badge.svg)](https://github.com/skbkontur/nunit-extensions/actions) |
 
 ## Release Notes