Fix MSTEST0037 false positive for nullable count argument

[Copilot]

Assert.HasCount(int expected, ...) does not accept int?, so MSTEST0037 must not suggest replacing Assert.AreEqual(nullableCount, collection.Count) with Assert.HasCount(nullableCount, collection) — doing so produces a CS1503 compile error.

Changes

• UseProperAssertMethodsAnalyzer.cs — In RecognizeCountCheck, return CountCheckStatus.Unknown when expectedArgument.Type is a nullable value type in the HasCount branch. 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 WhenAssertAreEqualWithCollectionCountNonZeroNullableExpected verifying no diagnostic is raised for both patterns when the expected value is int?.

Example

int? count = 3;

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

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• x3yvsblobprodcus370.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/testfx/testfx/artifacts/bin/MSTest.Analyzers.UnitTests/Debug/net8.0/MSTest.Analyzers.UnitTests /home/REDACTED/work/testfx/testfx/artifacts/bin/MSTest.Analyzers.UnitTests/Debug/net8.0/MSTest.Analyzers.UnitTests --diagnostic --diagnostic-output-directory /home/REDACTED/work/testfx/testfx/artifacts/log/Debug --diagnostic-file-prefix MSTest.Analyzers.UnitTests_net8.0_Debug_x64 --diagnostic-verbosity trace --crashdump --hangdump --hangdump-timeout 15m --report-azdo --coverage --coverage-settings /home/REDACTED/work/testfx/testfx/test/coverage.config --coverage-output MSTest.Analyzers.UnitTests_net8.0_Debug_x64.coverage --filter WhenAssertAreEqualWithCollectionCountNonZero (dns block)
  • Triggering command: /home/REDACTED/work/testfx/testfx/artifacts/bin/MSTest.Analyzers.UnitTests/Debug/net8.0/MSTest.Analyzers.UnitTests /home/REDACTED/work/testfx/testfx/artifacts/bin/MSTest.Analyzers.UnitTests/Debug/net8.0/MSTest.Analyzers.UnitTests --diagnostic --diagnostic-output-directory /home/REDACTED/work/testfx/testfx/artifacts/log/Debug --diagnostic-file-prefix MSTest.Analyzers.UnitTests_net8.0_Debug_x64 --diagnostic-verbosity trace --crashdump --hangdump --hangdump-timeout 15m --report-azdo --coverage --coverage-settings /home/REDACTED/work/testfx/testfx/test/coverage.config --coverage-output MSTest.Analyzers.UnitTests_net8.0_Debug_x64.coverage --filter WhenAssertAreEqualWithCollectionCountZero (dns block)

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