fix: improve error messages for unresolved generic type arguments in test generation

[thomhurst]

This pull request improves generic test support and error messaging in the test engine and source generator

[thomhurst]

Summary

Improves error messages for generic tests and fixes detection of class-level data sources on generic types.

Critical Issues

None found ✅

Suggestions

1. Source Generator Change May Need Dual-Mode Verification

The source generator now detects class-level data sources on generic types via the hasClassDataSources check:

var hasClassDataSources = testMethod.IsGenericType && testMethod.TypeSymbol.GetAttributesIncludingBaseTypes()
    .Any(a => DataSourceAttributeHelper.IsDataSourceAttribute(a.AttributeClass));

Question: Does the reflection-based test discovery in TUnit.Engine handle this scenario correctly? According to TUnit's dual-mode rule, changes to test discovery logic should work identically in both source-gen and reflection modes.

The change appears to fix a bug where generic classes with class-level data sources weren't being detected properly. If this is a bug fix, the reflection path may need the same fix, or we should verify it already handles this case.

Reference: .claude/docs/mandatory-rules.md - Rule 1 (Dual-Mode Implementation)

2. Snapshot Testing

Since the source generator output has changed (new code path for hasClassDataSources), snapshot tests should be run:

dotnet test TUnit.Core.SourceGenerator.Tests

If snapshots changed, commit the .verified.txt files (never .received.txt).

Reference: .claude/docs/mandatory-rules.md - Rule 2 (Snapshot Testing)

3. Minor: InterceptorsNamespaces Change

The change to TUnit.Example.Asp.Net.TestProject.csproj adds an InterceptorsNamespaces property.

This seems unrelated to the PR's stated purpose (improving generic test error messages). Is this an incidental fix for a build issue, or should it be in a separate commit?

Verdict

💬 COMMENT - Excellent error message improvements! Just want to verify dual-mode compatibility and snapshot testing.