Analyzer implementation to enhance assertions

src/Analyzers/MSTest.Analyzers/UseProperAssertMethodsAnalyzer.cs

@@ -125,6 +125,19 @@ private enum CountCheckStatus
         HasCount,
     }
 
+    private enum LinqPredicateCheckStatus
+    {
+        Unknown,
+        Any,
+        Count,
+        WhereAny,
+        WhereCount,
+        Single,
+        SingleOrDefault,
+        WhereSingle,
+        WhereSingleOrDefault,
+    }
+
     internal const string ProperAssertMethodNameKey = nameof(ProperAssertMethodNameKey);
 
     /// <summary>
@@ -268,6 +281,56 @@ private static void AnalyzeInvocationOperation(OperationAnalysisContext context,
             case "AreNotEqual":
                 AnalyzeAreEqualOrAreNotEqualInvocation(context, firstArgument, isAreEqualInvocation: false, objectTypeSymbol);
                 break;
+            case "IsNull":
+                AnalyzeIsNullOrIsNotNullInvocation(context, firstArgument, isNullCheck: true);
+                break;
+
+            case "IsNotNull":
+                AnalyzeIsNullOrIsNotNullInvocation(context, firstArgument, isNullCheck: false);
+                break;
+        }
+    }
+
+    private static void AnalyzeIsNullOrIsNotNullInvocation(OperationAnalysisContext context, IOperation argument, bool isNullCheck)
+    {
+        RoslynDebug.Assert(context.Operation is IInvocationOperation, "Expected IInvocationOperation.");
+
+        // Check for Single/SingleOrDefault patterns
+        LinqPredicateCheckStatus linqStatus = RecognizeLinqPredicateCheck(
+            argument,
+            out SyntaxNode? linqCollectionExpr,
+            out SyntaxNode? predicateExpr,
+            out _);
+
+        if (linqStatus is LinqPredicateCheckStatus.Single or
+                         LinqPredicateCheckStatus.SingleOrDefault or
+                         LinqPredicateCheckStatus.WhereSingle or
+                         LinqPredicateCheckStatus.WhereSingleOrDefault &&
+            linqCollectionExpr != null)
+        {
+            // For Assert.IsNotNull(enumerable.Single[OrDefault](...)) -> Assert.ContainsSingle
+            // For Assert.IsNull(enumerable.Single[OrDefault](...)) -> Assert.DoesNotContain
+            string properAssertMethod = isNullCheck ? "DoesNotContain" : "ContainsSingle";
+
+            ImmutableDictionary<string, string?>.Builder properties = ImmutableDictionary.CreateBuilder<string, string?>();
+            properties.Add(ProperAssertMethodNameKey, properAssertMethod);
+            properties.Add(CodeFixModeKey, predicateExpr != null ? CodeFixModeAddArgument : CodeFixModeSimple);
+
+            ImmutableArray<Location> additionalLocations = predicateExpr != null
+                ? ImmutableArray.Create(
+                    argument.Syntax.GetLocation(),
+                    predicateExpr.GetLocation(),
+                    linqCollectionExpr.GetLocation())
+                : ImmutableArray.Create(
+                    argument.Syntax.GetLocation(),
+                    linqCollectionExpr.GetLocation());
+
+            context.ReportDiagnostic(context.Operation.CreateDiagnostic(
+                Rule,
+                additionalLocations: additionalLocations,
+                properties: properties.ToImmutable(),
+                properAssertMethod,
+                isNullCheck ? "IsNull" : "IsNotNull"));
         }
     }
 
@@ -519,6 +582,146 @@ private static ComparisonCheckStatus RecognizeComparisonCheck(
         return ComparisonCheckStatus.Unknown;
     }
 
+    private static LinqPredicateCheckStatus RecognizeLinqPredicateCheck(
+    IOperation operation,
+    out SyntaxNode? collectionExpression,
+    out SyntaxNode? predicateExpression,
+    out IOperation? countOperation)
+    {
+        collectionExpression = null;
+        predicateExpression = null;
+        countOperation = null;
+
+        // Check for enumerable.Any(predicate)
+        // Extension methods appear as: Instance=null, Arguments[0]=collection, Arguments[1]=predicate
+        if (operation is IInvocationOperation anyInvocation &&
+            anyInvocation.TargetMethod.Name == "Any" &&
+            anyInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            anyInvocation.Arguments.Length == 2)
+        {
+            collectionExpression = anyInvocation.Arguments[0].Value.Syntax;
+            predicateExpression = anyInvocation.Arguments[1].Value.Syntax;
+            return LinqPredicateCheckStatus.Any;
+        }
+
+        // Check for enumerable.Count(predicate)
+        if (operation is IInvocationOperation countInvocation &&
+            countInvocation.TargetMethod.Name == "Count" &&
+            countInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            countInvocation.Arguments.Length == 2)
+        {
+            collectionExpression = countInvocation.Arguments[0].Value.Syntax;
+            predicateExpression = countInvocation.Arguments[1].Value.Syntax;
+            countOperation = operation;
+            return LinqPredicateCheckStatus.Count;
+        }
+
+        // Check for enumerable.Where(predicate).Any()
+        if (operation is IInvocationOperation whereAnyInvocation &&
+            whereAnyInvocation.TargetMethod.Name == "Any" &&
+            whereAnyInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereAnyInvocation.Arguments.Length == 1 &&
+            whereAnyInvocation.Arguments[0].Value is IInvocationOperation whereInvocation &&
+            whereInvocation.TargetMethod.Name == "Where" &&
+            whereInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereInvocation.Arguments.Length == 2)
+        {
+            collectionExpression = whereInvocation.Arguments[0].Value.Syntax;
+            predicateExpression = whereInvocation.Arguments[1].Value.Syntax;
+            return LinqPredicateCheckStatus.WhereAny;
+        }
+
+        // Check for enumerable.Where(predicate).Count()
+        if (operation is IInvocationOperation whereCountInvocation &&
+            whereCountInvocation.TargetMethod.Name == "Count" &&
+            whereCountInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereCountInvocation.Arguments.Length == 1 &&
+            whereCountInvocation.Arguments[0].Value is IInvocationOperation whereInvocation2 &&
+            whereInvocation2.TargetMethod.Name == "Where" &&
+            whereInvocation2.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereInvocation2.Arguments.Length == 2)
+        {
+            collectionExpression = whereInvocation2.Arguments[0].Value.Syntax;
+            predicateExpression = whereInvocation2.Arguments[1].Value.Syntax;
+            countOperation = operation;
+            return LinqPredicateCheckStatus.WhereCount;
+        }
+
+        // Check for enumerable.Where(predicate).Single()
+        if (operation is IInvocationOperation whereSingleInvocation &&
+            whereSingleInvocation.TargetMethod.Name == "Single" &&
+            whereSingleInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereSingleInvocation.Arguments.Length == 1 &&
+            whereSingleInvocation.Arguments[0].Value is IInvocationOperation whereInvocation3 &&
+            whereInvocation3.TargetMethod.Name == "Where" &&
+            whereInvocation3.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereInvocation3.Arguments.Length == 2)
+        {
+            collectionExpression = whereInvocation3.Arguments[0].Value.Syntax;
+            predicateExpression = whereInvocation3.Arguments[1].Value.Syntax;
+            return LinqPredicateCheckStatus.WhereSingle;
+        }
+
+        // Check for enumerable.Where(predicate).SingleOrDefault()
+        if (operation is IInvocationOperation whereSingleOrDefaultInvocation &&
+            whereSingleOrDefaultInvocation.TargetMethod.Name == "SingleOrDefault" &&
+            whereSingleOrDefaultInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereSingleOrDefaultInvocation.Arguments.Length == 1 &&
+            whereSingleOrDefaultInvocation.Arguments[0].Value is IInvocationOperation whereInvocation4 &&
+            whereInvocation4.TargetMethod.Name == "Where" &&
+            whereInvocation4.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable" &&
+            whereInvocation4.Arguments.Length == 2)
+        {
+            collectionExpression = whereInvocation4.Arguments[0].Value.Syntax;
+            predicateExpression = whereInvocation4.Arguments[1].Value.Syntax;
+            return LinqPredicateCheckStatus.WhereSingleOrDefault;
+        }
+
+        // Check for enumerable.Single(predicate)
+        if (operation is IInvocationOperation singleInvocation &&
+            singleInvocation.TargetMethod.Name == "Single" &&
+            singleInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable")
+        {
+            if (singleInvocation.Arguments.Length == 2)
+            {
+                // Extension method with predicate
+                collectionExpression = singleInvocation.Arguments[0].Value.Syntax;
+                predicateExpression = singleInvocation.Arguments[1].Value.Syntax;
+                return LinqPredicateCheckStatus.Single;
+            }
+            else if (singleInvocation.Arguments.Length == 1)
+            {
+                // Instance method or extension without predicate
+                collectionExpression = singleInvocation.Instance?.Syntax ?? singleInvocation.Arguments[0].Value.Syntax;
+                predicateExpression = null;
+                return LinqPredicateCheckStatus.Single;
+            }
+        }
+
+        // Check for enumerable.SingleOrDefault(predicate)
+        if (operation is IInvocationOperation singleOrDefaultInvocation &&
+            singleOrDefaultInvocation.TargetMethod.Name == "SingleOrDefault" &&
+            singleOrDefaultInvocation.TargetMethod.ContainingType?.ToDisplayString() == "System.Linq.Enumerable")
+        {
+            if (singleOrDefaultInvocation.Arguments.Length == 2)
+            {
+                // Extension method with predicate
+                collectionExpression = singleOrDefaultInvocation.Arguments[0].Value.Syntax;
+                predicateExpression = singleOrDefaultInvocation.Arguments[1].Value.Syntax;
+                return LinqPredicateCheckStatus.SingleOrDefault;
+            }
+            else if (singleOrDefaultInvocation.Arguments.Length == 1)
+            {
+                // Instance method or extension without predicate
+                collectionExpression = singleOrDefaultInvocation.Instance?.Syntax ?? singleOrDefaultInvocation.Arguments[0].Value.Syntax;
+                predicateExpression = null;
+                return LinqPredicateCheckStatus.SingleOrDefault;
+            }
+        }
+
+        return LinqPredicateCheckStatus.Unknown;
+    }
+
     private static void AnalyzeIsTrueOrIsFalseInvocation(OperationAnalysisContext context, IOperation conditionArgument, bool isTrueInvocation, INamedTypeSymbol objectTypeSymbol)
     {
         RoslynDebug.Assert(context.Operation is IInvocationOperation, "Expected IInvocationOperation.");
@@ -555,6 +758,36 @@ private static void AnalyzeIsTrueOrIsFalseInvocation(OperationAnalysisContext co
             return;
         }
 
+        // Check for LINQ predicate patterns that suggest Contains/DoesNotContain
+        LinqPredicateCheckStatus linqStatus = RecognizeLinqPredicateCheck(
+            conditionArgument,
+            out SyntaxNode? linqCollectionExpr,
+            out SyntaxNode? predicateExpr,
+            out _);
+
+        if (linqStatus != LinqPredicateCheckStatus.Unknown && linqCollectionExpr != null && predicateExpr != null)
+        {
+            // For Any() and Where().Any() patterns
+            if (linqStatus is LinqPredicateCheckStatus.Any or LinqPredicateCheckStatus.WhereAny)
+            {
+                string properAssertMethod = isTrueInvocation ? "Contains" : "DoesNotContain";
+
+                ImmutableDictionary<string, string?>.Builder properties = ImmutableDictionary.CreateBuilder<string, string?>();
+                properties.Add(ProperAssertMethodNameKey, properAssertMethod);
+                properties.Add(CodeFixModeKey, CodeFixModeAddArgument);
+                context.ReportDiagnostic(context.Operation.CreateDiagnostic(
+                    Rule,
+                    additionalLocations: ImmutableArray.Create(
+                        conditionArgument.Syntax.GetLocation(),
+                        predicateExpr.GetLocation(),
+                        linqCollectionExpr.GetLocation()),
+                    properties: properties.ToImmutable(),
+                    properAssertMethod,
+                    isTrueInvocation ? "IsTrue" : "IsFalse"));
+                return;
+            }
+        }
+
         // Check for string method patterns: myString.StartsWith/EndsWith/Contains(...)
         StringMethodCheckStatus stringMethodStatus = RecognizeStringMethodCheck(conditionArgument, out SyntaxNode? stringExpr, out SyntaxNode? substringExpr);
         if (stringMethodStatus != StringMethodCheckStatus.Unknown)
@@ -624,6 +857,54 @@ private static void AnalyzeIsTrueOrIsFalseInvocation(OperationAnalysisContext co
             return;
         }
 
+        // Special-case: enumerable.Count(predicate) > 0 → Assert.Contains(predicate, enumerable)
+        if (conditionArgument is IBinaryOperation binaryOp &&
+            binaryOp.OperatorKind == BinaryOperatorKind.GreaterThan)
+        {
+            if (binaryOp.LeftOperand is IInvocationOperation countInvocation &&
+                binaryOp.RightOperand.ConstantValue.HasValue &&
+                binaryOp.RightOperand.ConstantValue.Value is int intValue &&
+                intValue == 0 &&
+                countInvocation.TargetMethod.Name == "Count")
+            {
+                SyntaxNode? countCollectionExpr = null;
+                SyntaxNode? countPredicateExpr = null;
+
+                if (countInvocation.Instance != null && countInvocation.Arguments.Length == 1)
+                {
+                    countCollectionExpr = countInvocation.Instance.Syntax;
+                    countPredicateExpr = countInvocation.Arguments[0].Value.Syntax;
+                }
+                else if (countInvocation.Instance == null && countInvocation.Arguments.Length == 2)
+                {
+                    countCollectionExpr = countInvocation.Arguments[0].Value.Syntax;
+                    countPredicateExpr = countInvocation.Arguments[1].Value.Syntax;
+                }
+
+                if (countCollectionExpr != null && countPredicateExpr != null)
+                {
+                    string properAssertMethod = isTrueInvocation ? "Contains" : "DoesNotContain";
+
+                    ImmutableDictionary<string, string?>.Builder properties = ImmutableDictionary.CreateBuilder<string, string?>();
+                    properties.Add(ProperAssertMethodNameKey, properAssertMethod);
+                    properties.Add(CodeFixModeKey, CodeFixModeAddArgument);
+
+                    context.ReportDiagnostic(
+                        context.Operation.CreateDiagnostic(
+                            Rule,
+                            additionalLocations: ImmutableArray.Create(
+                                conditionArgument.Syntax.GetLocation(),
+                                countPredicateExpr.GetLocation(),
+                                countCollectionExpr.GetLocation()),
+                            properties: properties.ToImmutable(),
+                            properAssertMethod,
+                            isTrueInvocation ? "IsTrue" : "IsFalse"));
+
+                    return;
+                }
+            }
+        }
+
         // Check for comparison patterns: a > b, a >= b, a < b, a <= b
         ComparisonCheckStatus comparisonStatus = RecognizeComparisonCheck(conditionArgument, out SyntaxNode? leftExpr, out SyntaxNode? rightExpr);
         if (comparisonStatus != ComparisonCheckStatus.Unknown)
@@ -722,6 +1003,40 @@ private static void AnalyzeAreEqualOrAreNotEqualInvocation(OperationAnalysisCont
         {
             if (TryGetSecondArgumentValue((IInvocationOperation)context.Operation, out IOperation? actualArgumentValue))
             {
+                // Check for LINQ predicate patterns that suggest ContainsSingle
+                LinqPredicateCheckStatus linqStatus2 = RecognizeLinqPredicateCheck(
+                    actualArgumentValue!,
+                    out SyntaxNode? linqCollectionExpr2,
+                    out SyntaxNode? predicateExpr2,
+                    out _);
+
+                if (isAreEqualInvocation &&
+                    linqStatus2 is LinqPredicateCheckStatus.Count or LinqPredicateCheckStatus.WhereCount &&
+                    linqCollectionExpr2 != null &&
+                    predicateExpr2 != null &&
+                    expectedArgument.ConstantValue.HasValue &&
+                    expectedArgument.ConstantValue.Value is int expectedCountValue &&
+                    expectedCountValue == 1)
+                {
+                    // We have Assert.AreEqual(1, enumerable.Count(predicate))
+                    // We want Assert.ContainsSingle(predicate, enumerable)
+                    string properAssertMethod = "ContainsSingle";
+
+                    ImmutableDictionary<string, string?>.Builder properties = ImmutableDictionary.CreateBuilder<string, string?>();
+                    properties.Add(ProperAssertMethodNameKey, properAssertMethod);
+                    properties.Add(CodeFixModeKey, CodeFixModeAddArgument);
+                    context.ReportDiagnostic(context.Operation.CreateDiagnostic(
+                        Rule,
+                        additionalLocations: ImmutableArray.Create(
+                            actualArgumentValue.Syntax.GetLocation(),
+                            predicateExpr2.GetLocation(),
+                            linqCollectionExpr2.GetLocation()),
+                        properties: properties.ToImmutable(),
+                        properAssertMethod,
+                        "AreEqual"));
+                    return;
+                }
+
                 // Check if we're comparing a count/length property
                 CountCheckStatus countStatus = RecognizeCountCheck(
                     expectedArgument,

test/IntegrationTests/MSTest.IntegrationTests/OutputTests.cs

@@ -84,7 +84,8 @@ private static void ValidateOutputIsNotMixed(IEnumerable<TestResult> testResults
         Assert.Contains(methodName, message.Text);
         Assert.Contains("TestInitialize", message.Text);
         Assert.Contains("TestCleanup", message.Text);
-        Assert.IsFalse(shouldNotContain.Any(message.Text.Contains));
+        // Assert.IsFalse(shouldNotContain.Any(message.Text.Contains));
+        Assert.DoesNotContain(message.Text.Contains, shouldNotContain);
     }
 
     private static void ValidateInitializeAndCleanup(IEnumerable<TestResult> testResults, Func<TestResultMessage, bool> messageFilter)