Fix empty stack traces in release mode when using Microsoft Testing Platform

[Copilot]

Problem

Stack traces were empty or null in release mode when using Microsoft Testing Platform (MTP), causing test assertions that validate stack trace content to fail. This forced tests to be wrapped with #if DEBUG conditionals as a workaround.

Root Cause

The issue was that VSTest's testhost.exe.config includes a critical AppContext switch:

<AppContextSwitchOverrides value="Switch.System.Diagnostics.IgnorePortablePDBsInStackTraces=false" />

This setting allows portable PDBs to be used for stack traces. When this switch is not set (default is true), portable PDBs are ignored and stack traces appear empty in release builds. Microsoft Testing Platform didn't set this AppContext switch, causing the discrepancy between debug and release behavior.

Solution

1. Core Fix: Added AppContext.SetSwitch("Switch.System.Diagnostics.IgnorePortablePDBsInStackTraces", false) to the TestApplication static constructor in Microsoft.Testing.Platform. This ensures portable PDBs are used for stack traces, matching VSTest behavior.

2. Test Fixes: Systematically removed #if DEBUG conditionals from stack trace validation tests, including:

   • Critical test infrastructure in CLITestBase.e2e.cs used throughout the test suite
   • Unit tests in TestAssemblyInfoTests, TestMethodInfoTests, and TestClassInfoTests
   • Re-enabled integration tests that were disabled due to stack trace issues

Validation

Manual testing confirmed that:

• Stack traces are now generated correctly in release builds
• The AppContext switch works as expected with portable PDBs
• Previously failing stack trace assertions now pass in both debug and release modes

The fix is minimal, targeted, and ensures consistent behavior between debug and release builds while matching the established VSTest behavior.

Fixes #5109.

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