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perf: skip intermediate Dictionary alloc in CloneForDataDrivenIteration by @Evangelink in #9637 (backport to rel/4.3) #9639

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Merged
Evangelink merged 2 commits into from
Jul 5, 2026
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perf: skip intermediate Dictionary alloc in CloneForDataDrivenIteration by @Evangelink in #9637 (backport to rel/4.3) #9639

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perf: skip intermediate Dictionary alloc in CloneForDataDrivenIteration
Evangelink Jul 5, 2026
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Evangelink Jul 5, 2026
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15 changes: 8 additions & 7 deletions src/Adapter/MSTestAdapter.PlatformServices/Services/TestContextImplementation.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -524,13 +524,14 @@ private SynchronizedStringBuilder GetTestContextMessagesStringBuilder()
/// <returns>A fresh context suitable for one folded data-driven iteration.</returns>
internal TestContextImplementation CloneForDataDrivenIteration()
{
// Pass testMethod: null and testClassFullName: null because the relevant labels
// (including TestNameLabel / FullyQualifiedTestClassNameLabel and anything merged from
// AssemblyInitialize / ClassInitialize) are already in _properties. In that branch the
// constructor takes a shallow copy of the passed dictionary, so passing _properties
// directly gives the clone an isolated property bag without an extra intermediate copy:
// per-iteration mutations to the clone's property bag won't leak back to this instance
// nor to subsequent iterations.
// Pass _properties directly and testMethod: null / testClassFullName: null because the
// relevant labels (including TestNameLabel / FullyQualifiedTestClassNameLabel and anything
// merged from AssemblyInitialize / ClassInitialize) are already in the property bag. The
// constructor's null/null branch copies the supplied properties into a fresh dictionary
// via the [with(properties)] spread, so no intermediate snapshot allocation is needed and
// isolation is preserved: per-iteration mutations to the clone's property bag won't leak
// back to this instance nor to subsequent iterations, and mutations to this instance after
// clone creation won't leak into the clone.
var clone = new TestContextImplementation(testMethod: null, testClassFullName: null, _properties, _messageLogger, _testRunCancellationToken);

// Preserve TestRunCount so user code that observes it (e.g. retry-aware tests) sees
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