[file-diet] Refactor `Assert.ThrowsException.cs` (832 lines) into focused partial-class files

[Evangelink]

Overview

The file src/TestFramework/TestFramework/Assertions/Assert.ThrowsException.cs has grown to 832 lines, making it harder to navigate and maintain. This task involves refactoring it into smaller, more focused partial-class files — following the same pattern already used throughout the Assert type.

Note: The technically-largest file (XxHashShared.cs, 911 lines) was intentionally skipped as it is a verbatim port of .NET runtime code and should not be modified here.

Current State

• File: src/TestFramework/TestFramework/Assertions/Assert.ThrowsException.cs
• Size: 832 lines
• Language: C#

Structural Analysis

The file contains four distinct concerns bundled into a single partial-class file:

Lines	Content
28–157	AssertNonStrictThrowsInterpolatedStringHandler<TException> struct — lazy-evaluation ISH for Assert.Throws
159–290	AssertThrowsExactlyInterpolatedStringHandler<TException> struct — lazy-evaluation ISH for Assert.ThrowsExactly
291–388	Public Throws<TException> sync overloads (string, Func<Exception?,string>, interpolated-string-handler forms)
389–482	Public ThrowsExactly<TException> sync overloads (same three forms)
483–610	Public ThrowsAsync<TException> and ThrowsExactlyAsync<TException> overloads
611–789	Private implementation: ThrowsException, ThrowsExceptionAsync, IsThrowsFailing, IsThrowsAsyncFailingAsync, ReportThrowsFailed, GetDisplayTypeName
790–832	Private support types: ThrowsFailureKind enum, ThrowsExceptionState struct, GetTrackedThrowsName helper

The interpolated-string-handler structs alone account for ~270 lines and are the primary driver of file size.

Refactoring Strategy

Proposed File Splits

Split the file into three focused partial-class files inside src/TestFramework/TestFramework/Assertions/:

1. Assert.ThrowsException.InterpolatedStringHandlers.cs (~270 lines)

   • Contents: AssertNonStrictThrowsInterpolatedStringHandler<TException>, AssertThrowsExactlyInterpolatedStringHandler<TException>
   • Responsibility: Compiler-facing interpolated-string-handler structs that enable deferred message formatting; these are purely infrastructure and benefit from being read in isolation

2. Assert.ThrowsException.cs (~270 lines, trimmed from current 832)

   • Contents: All public Throws<TException> and ThrowsExactly<TException> sync overloads, all public ThrowsAsync<TException> and ThrowsExactlyAsync<TException> overloads
   • Responsibility: The public assertion API surface — what test authors actually call

3. Assert.ThrowsException.Core.cs (~220 lines)

   • Contents: ThrowsException / ThrowsExceptionAsync private dispatch helpers, IsThrowsFailing / IsThrowsAsyncFailingAsync, ReportThrowsFailed, GetDisplayTypeName, ThrowsFailureKind enum, ThrowsExceptionState struct, GetTrackedThrowsName
   • Responsibility: Private implementation shared by all public overloads; keeping it separate makes the public API file noise-free

Implementation Guidelines

1. Preserve Behavior: All existing functionality must work identically after the split
2. Maintain Public API: Keep all public AssertNonStrictThrowsInterpolatedStringHandler<TException> and AssertThrowsExactlyInterpolatedStringHandler<TException> symbols exactly as-is (they are referenced in [InterpolatedStringHandlerArgument] attributes in callers)
3. Partial class continuity: Each new file must declare public sealed partial class Assert in namespace Microsoft.VisualStudio.TestTools.UnitTesting
4. No import changes needed: All files share the same namespace; no using directives reference these types from the outside
5. Test After Each Split: Run ./build.sh -test after each incremental move to confirm nothing breaks
6. One File at a Time: Move the ISH structs first, then the core helpers, to keep diffs reviewable

Acceptance Criteria

• Original file is split into three focused partial-class files
• Each new file is under 300 lines
• All tests pass after refactoring (./build.sh -test)
• No breaking changes to public API (PublicAPI.Unshipped.txt unchanged or updated correctly)
• The #pragma warning disable RS0026 at the top of the original file is retained in the file(s) that still carry the affected overloads

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Priority: Medium
Effort: Small
Expected Impact: Improved code navigability, easier code review, reduced cognitive load when working on a single concern (e.g., only the ISH structs or only the async overloads)

🤖 Automated content by GitHub Copilot. Posted via a maintainer's GitHub token, so it appears under their account — the account owner did not write or approve this content personally. Generated by the Daily File Diet workflow. · 159.7 AIC · ⌖ 13.1 AIC · [◷]( · ◷)

• expires on Jun 14, 2026, 7:35 PM UTC

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