🏋️ File Diet: Refactor `TestMethodInfo.cs` (1113 lines) into focused modules

[Evangelink]

Overview

The file src/Adapter/MSTestAdapter.PlatformServices/Execution/TestMethodInfo.cs has grown to 1113 lines, making it harder to navigate and maintain. This task involves refactoring it into smaller, more focused files.

Current State

• File: src/Adapter/MSTestAdapter.PlatformServices/Execution/TestMethodInfo.cs
• Size: 1113 lines
• Language: C#

Structural Analysis

The file contains a single TestMethodInfo class that has accumulated several distinct responsibilities:

Lines	Concern
~23–168	Core class definition, properties, InvokeAsync entry point
~169–329	Argument resolution (ResolveArguments, SetArguments)
~250–329	Timeout resolution (GetTestTimeout, ThrowMultipleAttributesException)
~330–521	Main test execution loop (ExecuteInternalAsync)
~522–597	Exception handling (HandleMethodException)
~598–782	TestCleanup lifecycle (RunTestCleanupMethodAsync, HasCleanupsToInvoke)
~705–857	TestInitialize lifecycle (RunTestInitializeMethodAsync, InvokeInitializeMethodAsync, InvokeGlobalInitializeMethodAsync)
~857–958	Global cleanup invocation (InvokeGlobalCleanupMethodAsync, CaptureExecutionContextAfterFixtureIfNeeded)
~959–1005	TestContext setup (SetTestContext)
~1006–1113	Timeout-aware execution (ExecuteInternalWithTimeoutAsync)

Refactoring Strategy

Since TestMethodInfo is a single class (not multiple classes) and C# supports partial class, the most idiomatic approach for this codebase is to split the implementation into partial class files, each focusing on a specific aspect of test method execution.

Proposed File Splits

1. TestMethodInfo.cs (keep, trimmed)

   • Contents: Class declaration, fields, properties, constructor, public InvokeAsync entry point
   • Responsibility: Core identity and public API surface (~150 lines)

2. TestMethodInfo.ArgumentResolution.cs (new partial class)

   • Contents: SetArguments, ResolveArguments
   • Responsibility: Mapping data-driven test arguments to method parameters (~160 lines)

3. TestMethodInfo.Execution.cs (new partial class)

   • Contents: ExecuteInternalAsync, ExecuteInternalWithTimeoutAsync, GetTestTimeout, ThrowMultipleAttributesException
   • Responsibility: Core test body execution, timeout management (~300 lines)

4. TestMethodInfo.ExceptionHandling.cs (new partial class)

   • Contents: HandleMethodException
   • Responsibility: Mapping raw exceptions to TestFailedException with proper messages (~75 lines)

5. TestMethodInfo.Lifecycle.cs (new partial class)

   • Contents: RunTestInitializeMethodAsync, InvokeInitializeMethodAsync, InvokeGlobalInitializeMethodAsync, RunTestCleanupMethodAsync, InvokeCleanupMethodAsync, InvokeGlobalCleanupMethodAsync, HasCleanupsToInvoke, CaptureExecutionContextAfterFixtureIfNeeded
   • Responsibility: TestInitialize / TestCleanup fixture invocation (~430 lines)

6. TestMethodInfo.TestContext.cs (new partial class)

   • Contents: SetTestContext
   • Responsibility: Wiring ITestContext onto the class instance before test execution (~50 lines)

Implementation Guidelines

1. Preserve Behavior: All existing functionality must work identically after the split
2. Maintain Public API: Keep exported/public symbols accessible with the same names
3. Use partial class: C# partial classes avoid any need to change access modifiers or visibility
4. Test After Each Split: Run the test suite after each incremental file move
5. One File at a Time: Split one partial at a time to make review easier

Acceptance Criteria

• Original file is split into focused partial class files (one per concern)
• Each new file is under 300 lines
• All tests pass after refactoring
• No breaking changes to public API
• No changes to method signatures or access modifiers

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Priority: Medium
Effort: Medium
Expected Impact: Improved code navigability, easier per-concern testing, reduced merge conflicts on busy test execution code

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