Add explicit type tests for AvoidOutParameterOnAssertIsInstanceOfTypeFixer

[Evangelink]

Fixes #9874

Summary

AvoidOutParameterOnAssertIsInstanceOfTypeFixer.FixIsInstanceOfTypeCallAsync has two distinct code paths:

1. When the type is non-null (explicit type declaration like out string result) → creates a VariableDeclarationSyntax.
2. When the type is null (existing variable like out result) → creates an AssignmentExpression.

The out var result case was covered, but the explicit type case (e.g., out string result → string result = ...) was not tested.

Changes

Added two tests to AvoidOutParameterOnAssertIsInstanceOfTypeFixerTests.cs:

• FixIsInstanceOfTypeWithExplicitType_ShouldProduceTypedVariableDeclaration — out string result → string result = Assert.IsInstanceOfType<string>(value) (with/without trivia, single and multi-instance).
• FixIsInstanceOfTypeWithExplicitTypeAndMessage_ShouldProduceTypedVariableDeclaration — same with a message argument.

Verification

• Build succeeded (0 warnings, 0 errors).
• All 8 tests in the class pass (6 existing + 2 new) on net8.0.

[Copilot]

Pull request overview

Adds explicit-type coverage for the analyzer code fix that converts invalid out string result assertions into typed variable declarations.

Changes:

• Tests conversion with and without message arguments.
• Verifies trivia preservation and multiple occurrences.

Show a summary per file

File	Description
test/UnitTests/MSTest.Analyzers.UnitTests/AvoidOutParameterOnAssertIsInstanceOfTypeFixerTests.cs	Adds explicit-type code-fix tests.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Medium

[github-actions]

🧪 Test quality grade — PR #9885

Grade	Test	Notes
A (90–100)	new AvoidOutParameterOnAssertIsInstanceOfTypeFixerTests. FixIsInstanceOfTypeWithExplicitTypeAndMessage_ ShouldProduceTypedVariableDeclaration	Clear AAA; VerifyCodeFixAsync strongly asserts the exact code transformation for the message-overload case.
B (80–89)	new AvoidOutParameterOnAssertIsInstanceOfTypeFixerTests. FixIsInstanceOfTypeWithExplicitType_ ShouldProduceTypedVariableDeclaration	Strong assertion via VerifyCodeFixAsync; body is ~50 lines due to two embedded code-literal fixtures — consider splitting into two focused tests (one per method in the fixture).

_{This advisory comment was generated automatically. Grades are heuristic
and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 34.1 AIC · ⌖ 5.7 AIC · ⊞ 9.6K · [◷]( · ◷)

[github-actions]

LGTM — Clean, well-structured tests that fill a real coverage gap for the explicit-type code path in FixIsInstanceOfTypeCallAsync. The trivia preservation and multi-instance scenarios are good additions. No issues found.