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perf: skip intermediate Dictionary alloc in CloneForDataDrivenIteration#9637

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Merged
Amaury Levé (Evangelink) merged 1 commit into from
Jul 5, 2026
Merged

perf: skip intermediate Dictionary alloc in CloneForDataDrivenIteration #9637

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19 changes: 9 additions & 10 deletions src/Adapter/MSTestAdapter.PlatformServices/Services/TestContextImplementation.cs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -524,16 +524,15 @@ private SynchronizedStringBuilder GetTestContextMessagesStringBuilder()
/// <returns>A fresh context suitable for one folded data-driven iteration.</returns>
internal TestContextImplementation CloneForDataDrivenIteration()
{
// Take a shallow snapshot of the current property bag so that the clone starts with
// the same properties (including TestNameLabel / FullyQualifiedTestClassNameLabel and
// anything merged from AssemblyInitialize / ClassInitialize) but is otherwise isolated.
// Per-iteration mutations to the clone's property bag won't leak back to this instance
// nor to subsequent iterations.
var snapshot = new Dictionary<string, object?>(_properties);

// Pass testMethod: null and testClassFullName: null because the relevant labels are
// already in the snapshot. The constructor will copy the snapshot as-is.
var clone = new TestContextImplementation(testMethod: null, testClassFullName: null, snapshot, _messageLogger, _testRunCancellationToken);
// 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
// the same value it would see in the unfolded path. TestRunCount represents the
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