Fix MSTEST0037 false positive for non-int count argument

[Copilot]

Assert.HasCount(int expected, ...) only accepts int, so MSTEST0037 must not suggest replacing Assert.AreEqual(expected, collection.Count) with Assert.HasCount(expected, collection) when the expected argument is not int — doing so produces a CS1503 compile error.

Changes

• UseProperAssertMethodsAnalyzer.cs — In RecognizeCountCheck, return CountCheckStatus.Unknown when expectedArgument.Type?.SpecialType != SpecialType.System_Int32 in the HasCount branch. This covers all non-int types including int?, long, uint, decimal, etc. Applies to both the BCL .Count/.Length property pattern and the LINQ .Count() method pattern. The IsEmpty branch (expected == 0) is unaffected since the expected argument is removed entirely by the fix.
• UseProperAssertMethodsAnalyzerTests.cs — Add WhenAssertAreEqualWithCollectionCountNonZeroNonIntExpected verifying no diagnostic is raised for both patterns when the expected value is int? or long.

Example

int? nullableCount = 3;
long longCount = 3L;

// Before: MSTEST0037 fired, fixer produced Assert.HasCount(count, list) → CS1503
// After: no diagnostic
Assert.AreEqual(nullableCount, list.Count);
Assert.AreEqual(nullableCount, list.AsEnumerable().Count());
Assert.AreEqual(longCount, list.Count);
Assert.AreEqual(longCount, list.AsEnumerable().Count());

---

💬 Send tasks to Copilot coding agent from Slack and Teams to turn conversations into code. Copilot posts an update in your thread when it's finished.

[Copilot]

Pull request overview

Fixes MSTEST0037 (UseProperAssertMethodsAnalyzer) incorrectly suggesting Assert.HasCount(expected, collection) when the expected count is a nullable value type (e.g., int?), which would otherwise lead to a CS1503 compile error after applying the code fix.

Changes:

• Update RecognizeCountCheck to return CountCheckStatus.Unknown for the HasCount suggestion when expectedArgument.Type is a nullable value type, for both .Count/.Length and LINQ .Count() patterns.
• Add a unit test ensuring no MSTEST0037 diagnostic is produced for Assert.AreEqual(int?, collection.Count) and Assert.AreEqual(int?, enumerable.Count()).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Analyzers/MSTest.Analyzers/UseProperAssertMethodsAnalyzer.cs	Suppresses HasCount suggestion when the expected argument is nullable to avoid non-compiling fixes.
test/UnitTests/MSTest.Analyzers.UnitTests/UseProperAssertMethodsAnalyzerTests.cs	Adds coverage for nullable expected count (both property and LINQ Count patterns).

Comments suppressed due to low confidence (1)

src/Analyzers/MSTest.Analyzers/UseProperAssertMethodsAnalyzer.cs:1482

• Same as above for the LINQ Count() pattern: returning HasCount without validating that expectedArgument.Type can be passed to Assert.HasCount(int, ...) can lead to diagnostics/code fixes that don't compile when expected is a non-int numeric type. Suggest checking implicit conversion to int (or restricting to appropriate integral types) before returning HasCount.

                // Assert.HasCount takes int, not int?, so skip if expectedCount is a nullable value type.
                if (expectedArgument.Type.IsNullableValueType())
                {
                    nodeToBeReplaced1 = null;
                    replacement1 = null;
                    nodeToBeReplaced2 = null;
                    replacement2 = null;
                    return CountCheckStatus.Unknown;
                }