[perf-improver] perf: single-pass message iteration in VSTestBridge ObjectModelConverters

[Evangelink]

🤖 This is an automated contribution from Perf Improver.

Goal and Rationale

When converting a VSTest TestResult to a TestNode in the VSTestBridge adapter, testResult.Messages was iterated twice when TRX reporting was enabled:

1. A LINQ Select pass to build a TrxMessage[] for TrxMessagesProperty — creates a SelectIterator<> state machine and an intermediate array via [.. ...] collection spread
2. A separate foreach to collect standardErrorMessages / standardOutputMessages for StandardErrorProperty / StandardOutputProperty

This also removes a dead addVSTestProviderProperties variable that was declared but its value was never read (the call-site was removed at some earlier point).

Approach

Replace the two separate iterations with a single foreach that builds all three collections in one pass:

• When isTrxEnabled, transform each message to a TrxMessage and collect it in a pre-allocated List<TrxMessage>
• Simultaneously collect standard-error and standard-output strings (as before)
• After the loop, use the collected List<TrxMessage> to create TrxMessagesProperty

Performance Evidence

Path	Before	After
testResult.Messages iterations (TRX enabled)	2 (LINQ Select + foreach)	1 (single foreach)
Allocations per call (TRX enabled)	SelectIterator<> + intermediate TrxMessage[] + dead bool + List<string>? × 2	List<TrxMessage> (pre-allocated) + List<string>? × 2
Allocations per call (TRX disabled)	dead bool + List<string>? × 2	List<string>? × 2

For a typical CI run with 1 000 tests and TRX enabled, this eliminates ≥1 000 SelectIterator state machines and ≥1 000 intermediate TrxMessage[] allocations.

Methodology: code inspection + diff review. ToTestNode(TestResult) is called once per test result in the VSTestBridge execution path.

Trade-offs

• Slightly more verbose loop body when TRX is enabled (explicit TrxMessage trxMsg = switch { ... }), but the logic is clearer than splitting across two separate iterations.
• No change to observable behaviour: the same properties are added in the same order.

Test Status

• Microsoft.Testing.Platform.UnitTests (net8.0): 1079 passed, 0 failed, 3 skipped ✅
• Microsoft.Testing.Extensions.UnitTests (net8.0): 392 passed, 0 failed, 7 skipped ✅
• Build: 0 warnings, 0 errors ✅

Reproducibility

./build.sh
artifacts/bin/Microsoft.Testing.Extensions.UnitTests/Debug/net8.0/Microsoft.Testing.Extensions.UnitTests

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[Copilot]

Pull request overview

This PR optimizes the VSTestBridge adapter’s conversion from VSTest TestResult to MTP TestNode by consolidating testResult.Messages processing into a single pass, reducing iterator/collection allocations when TRX reporting is enabled.

Changes:

• Replaces the prior Select(...)+[..] TRX message projection plus a separate foreach with a single foreach that collects TRX messages, stdout, and stderr together.
• Removes an unused addVSTestProviderProperties local that was computed but never read.

Show a summary per file

File	Description
src/Platform/Microsoft.Testing.Extensions.VSTestBridge/ObjectModel/ObjectModelConverters.cs	Consolidates message processing into one loop and removes a dead local to reduce allocations in the VSTestBridge conversion path.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[Evangelink]

🔍 Build Failure Analysis

Workflow run: https://github.com/microsoft/testfx/actions/runs/26975085514

❌ Root Cause: IDE0028 — Collection initialization can be simplified

The build fails with 3 errors (one per target framework: netstandard2.0, net8.0, net9.0), all pointing to the same single location:

src/Platform/Microsoft.Testing.Extensions.VSTestBridge/ObjectModel/ObjectModelConverters.cs(145,56): error IDE0028

The newly introduced line:

List<TrxMessage>? trxMessages = isTrxEnabled ? new List<TrxMessage>(testResult.Messages.Count) : null;

triggers IDE0028 ("Collection initialization can be simplified") because .editorconfig sets dotnet_style_prefer_collection_expression = true and the type List<TrxMessage> is redundant — it can be inferred from the left-hand side. In CI the project builds with /p:TreatWarningsAsErrors=true, promoting this warning to an error.

✅ Fix

Use a target-typed new expression to drop the redundant type annotation while preserving the capacity hint:

// Before (triggers IDE0028)
List<TrxMessage>? trxMessages = isTrxEnabled ? new List<TrxMessage>(testResult.Messages.Count) : null;

// After
List<TrxMessage>? trxMessages = isTrxEnabled ? new(testResult.Messages.Count) : null;

This is the minimal one-character change that satisfies the analyzer, keeps the pre-sizing optimisation intact (important on netstandard2.0 where EnsureCapacity is unavailable), and is idiomatic C#.

An inline suggestion has been posted directly on the offending line below.

Generated by Build Failure Analysis for issue #8823 · sonnet46 2.6M · ◷

[Evangelink]

Generated by Build Failure Analysis for issue #8823 · sonnet46 2.6M

[Copilot]

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1