Optimize TestMethodRunner: fix double enumeration, reduce allocations by Evangelink · Pull Request #7541 · microsoft/testfx

Evangelink · 2026-03-12T21:09:07Z

Fix double enumeration in TryExecuteFoldedDataDrivenTestsAsync by materializing GetData() into an IReadOnlyList once instead of calling .Any() then re-enumerating
Remove unnecessary List allocation in UpdateResultsWithParentInfo by mutating in place and returning void
Cache result[result.Length - 1] into a local in ExecuteAsync catch block
Skip redundant first-element self-comparison in GetAggregateOutcome
Use Stopwatch.StartNew() in ExecuteTestFromDataSourceAttributeAsync

- Fix double enumeration in TryExecuteFoldedDataDrivenTestsAsync by materializing GetData() into an IReadOnlyList once instead of calling .Any() then re-enumerating - Remove unnecessary List allocation in UpdateResultsWithParentInfo by mutating in place and returning void - Cache result[result.Length - 1] into a local in ExecuteAsync catch block - Skip redundant first-element self-comparison in GetAggregateOutcome - Use Stopwatch.StartNew() in ExecuteTestFromDataSourceAttributeAsync

- Hoist loop-invariant 'testContext as TestContextImplementation' cast above the foreach loop in RunAssemblyCleanupAsync - Remove unnecessary nested scope in IsTestMethodRunnable - Use 'is null' pattern instead of '== null' - Simplify ignore message logic by inlining into the conditional block

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Pull request overview

This PR optimizes TestMethodRunner execution paths in the MSTest adapter by reducing redundant work (enumerations/allocations) during data-driven execution and result aggregation.

Changes:

Materialize folded data-driven GetData() results once to avoid double enumeration and enable Count checks.
Remove an unnecessary list allocation by mutating results in place in UpdateResultsWithParentInfo.
Minor micro-optimizations (cache last result in exception path, skip redundant first element in aggregate outcome, use Stopwatch.StartNew()).

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src/Adapter/MSTestAdapter.PlatformServices/Execution/TestMethodRunner.cs

src/Adapter/MSTestAdapter.PlatformServices/Execution/UnitTestRunner.cs

src/Adapter/MSTestAdapter.PlatformServices/Execution/TestMethodRunner.cs

- Resolve merge conflict in TestMethodRunner.cs (take main's simplified catch block) - Fix GetData() double-call: enumerate once with bool flag instead of materializing to list - Fix UpdateResultsWithParentInfo XML doc to match actual behavior - Preserve ignore message behavior in UnitTestRunner.cs (add shouldIgnoreMethod guard)

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Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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src/Adapter/MSTestAdapter.PlatformServices/Execution/TestMethodRunner.cs

…path - Update comment in TestMethodRunner to reference AssemblyEnumerator.TryUnfoldITestDataSource - Update comment in AssemblyEnumerator to reference TestMethodRunner.TryExecuteFoldedDataDrivenTestsAsync - Apply same single-enumeration pattern in AssemblyEnumerator.TryUnfoldITestDataSource to avoid double-enumerating GetData()

Copilot AI review requested due to automatic review settings March 12, 2026 21:09

Evangelink enabled auto-merge March 12, 2026 21:09

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Copilot AI reviewed Mar 12, 2026

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