Add MSTEST0059: Detect conflicting Parallelize and DoNotParallelize attributes

[Copilot]

Add analyzer MSTEST0058 to prevent having both Parallelize and DoNotParallelize assembly attributes

Summary

This PR implements a new analyzer (MSTEST0058) that detects and reports a warning when an assembly has both [Parallelize] and [DoNotParallelize] attributes, which creates an ambiguous configuration.

Implementation Details

Analyzer Logic:

• MSTEST0058 checks for conflicting attributes first and reports regardless of test adapter presence
• Diagnostics are reported with locations pointing to both attribute declarations (on the attribute name itself)
• MSTEST0001 (missing attributes) only checks when test adapter is referenced

Test Coverage:

• Tests for both attributes present in same order
• Tests for both attributes present in different orders
• Tests cover scenarios with and without MSTest adapter referenced
• Tests expect diagnostics on both attribute locations (on the attribute names)
• Test for multiple attributes in same attribute list (e.g., [assembly: Parallelize(...), MyAsm])

Localization:

• Added Locked markers ({Locked="..."}) to resource strings to prevent translation of attribute names [Parallelize] and [DoNotParallelize]
• Fixed Locked format to use multiple {Locked=...} instead of comma-separated values

Documentation:

• Updated analyzer description to clarify that when both attributes are present, [DoNotParallelize] takes precedence and parallelization will be disabled

Bug Fix:

• Fixed logic so MSTEST0058 reports even when test adapter is not referenced
• Moved test adapter check to only apply to MSTEST0001 diagnostic

Improvements:

• Changed from no-location diagnostics to location-specific diagnostics on both conflicting attributes

• Users now see exactly where the conflicting attributes are declared, improving the developer experience

• Fixes MSTEST0001: Explicitly enable or disable tests parallelization #6822

Original prompt

---

This section details on the original issue you should resolve

<issue_title>MSTEST0001: Explicitly enable or disable tests parallelization</issue_title>
<issue_description>I don't know what to say but this warning is just stupid.

And the implementation allows to define [assembly: Microsoft.VisualStudio.TestTools.UnitTesting.DoNotParallelize] in one cs file and in another [assembly: Microsoft.VisualStudio.TestTools.UnitTesting.Parallelize]. So what setting is now chosen?</issue_description>

<agent_instructions>Create a new analyzer that will prevent having both assembly level attributes DoNotParallelize and Parallelize</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@Evangelink > I don't know what to say but this warning is just stupid.

@Balkoth thanks for the constructive feedback ;)

Jokes aside the rule is in place because we have seen many repositories that would benefit from having parallelism enabled but some cannot be enabled for reasons. Instead of simply staying in the limbo state, having explicit call and ideally comment about why it's not parallelisable is good.

And the implementation allows to define [assembly: Microsoft.VisualStudio.TestTools.UnitTesting.DoNotParallelize] in one cs file and in another [assembly: Microsoft.VisualStudio.TestTools.UnitTesting.Parallelize]. So what setting is now chosen?

Thank you! I hadn't realize this. I think short-term we should introduce an analyzer to guard against this case and mid-term we should probably consider merging attributes into a single one.</comment_new>

• Fixes MSTEST0001: Explicitly enable or disable tests parallelization #6822

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[Evangelink]

@copilot some tests are broken

test/UnitTests/MSTest.Analyzers.UnitTests/UseParallelizeAttributeAnalyzerTests.cs#L34

test/UnitTests/MSTest.Analyzers.UnitTests/UseParallelizeAttributeAnalyzerTests.cs(34,1): error : Test method MSTest.Analyzers.Test.UseParallelizeAttributeAnalyzerTests.WhenBothAttributesSetInDifferentOrder_Diagnostic threw exception:
System.InvalidOperationException: Context: Diagnostics of test state
Mismatch between number of diagnostics returned, expected "1" actual "0"

Diagnostics:
NONE.

[Copilot]

@copilot some tests are broken

test/UnitTests/MSTest.Analyzers.UnitTests/UseParallelizeAttributeAnalyzerTests.cs#L34...

Fixed in c458eb3. The issue was that the test adapter check was happening before the conflicting attributes check, preventing MSTEST0058 from being reported when the adapter wasn't referenced. I've reordered the logic so MSTEST0058 is now reported regardless of test adapter presence, while MSTEST0001 (missing attributes) still only reports when the adapter is referenced.

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