add deep inheritance chain for tests analyzer

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/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";
+    }
+}

NUnit.Extensions.Tests/Middlewares/ParallelTestFixtureSetUpTest.cs

@@ -21,8 +21,16 @@ public void Test()
         }
     }
 
+    public abstract class Base2 : SimpleTestBase
+    {
+    }
+
+    public abstract class Base3 : Base2
+    {
+    }
+
     [Parallelizable(ParallelScope.Self)]
-    public class SecondTestFixtureSetUpTest : SimpleTestBase
+    public class SecondTestFixtureSetUpTest : Base3
     {
         protected override void Configure(ISetupBuilder fixture, ISetupBuilder test)
         {