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[Efficiency Improver] perf: eliminate yield-iterator state machine in PropertyBag.OfType(T)() #7917

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Merged
Evangelink merged 3 commits into from
Apr 29, 2026
+58 −2
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[Efficiency Improver] perf: eliminate yield-iterator state machine in PropertyBag.OfType(T)() #7917

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8e95fc5
perf: eliminate yield-iterator state machine in PropertyBag.OfType<T>()
github-actions[bot] Apr 29, 2026
911b697
test: add coverage tests for OfType<T>() edge cases in PropertyBagTests
Copilot Apr 29, 2026
813c705
test: fix variable naming in PropertyBagTests for consistency
Copilot Apr 29, 2026
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33 changes: 31 additions & 2 deletions src/Platform/Microsoft.Testing.Platform/Messages/PropertyBag.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -274,9 +274,38 @@ public TProperty[] OfType<TProperty>()
}

// We don't want to allocate an array if we know that we're looking for a TestNodeStateProperty
return typeof(TestNodeStateProperty).IsAssignableFrom(typeof(TProperty))
if (typeof(TestNodeStateProperty).IsAssignableFrom(typeof(TProperty)) || _property is null)
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@github-actions github-actions Bot Apr 29, 2026

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[Coverage] The || _property is null branch is new (the original ternary had _property is null ? [] as its own arm). There's currently no test for calling OfType<SomeDummyProperty>() on a PropertyBag that contains only a TestNodeStateProperty (i.e., _testNodeStateProperty is set but _property is null).

Impact: The early-return path added here goes unverified. If a future refactor accidentally removes it, a silent linear walk over a null reference would produce incorrect results.

Suggestion: Add a test case to PropertyBagTests:

[TestMethod]
public void OfType_WithOnlyTestNodeStateProperty_ReturnsEmpty()
{
    PropertyBag property = new();
    property.Add(PassedTestNodeStateProperty.CachedInstance);
    // _property is null; _testNodeStateProperty is set — exercises the new early-return path
    Assert.IsEmpty(property.OfType<DummyProperty>());
}

{
return [];
}

// Direct linked-list walk: avoids allocating a yield-iterator state machine
// (the original code called _property.OfType<TProperty>() which uses yield return).
TProperty? first = default;
bool foundAny = false;
List<TProperty>? overflow = null;
Property? current = _property;
while (current is not null)
{
if (current.Current is TProperty match)
{
if (!foundAny)
{
first = match;
foundAny = true;
}
else
{
(overflow ??= [first!]).Add(match);
}
}

current = current.Next;
}

return !foundAny
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[Coverage] The !foundAny ? [] return at the end of the while-loop (no matching property found in a non-empty bag) is not tested. DummyProperty2 is used in Single / SingleOrDefault tests, but OfType<DummyProperty2>() is never called on a bag that has other properties.

Impact: The new manual traversal diverges from the old LINQ-based _property.OfType<TProperty>(). A bug that incorrectly returns null or throws instead of [] when no match is found would go undetected.

Suggestion: Add one assertion to the existing OfType_Should_Return_CorrectObject test:

// No DummyProperty2 in the bag — exercises the "no match found" path in the while-loop
Assert.IsEmpty(property.OfType<DummyProperty2>());

? []
: _property is null ? [] : [.. _property.OfType<TProperty>()];
: overflow is not null ? [.. overflow] : [first!];
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[Coverage] The single-item fast path ([first!] when overflow is null) is not exercised by any existing test. OfType_Should_Return_CorrectObject only tests with 2 DummyProperty instances, which goes through the overflow branch. The [first!] path needs its own case.

Impact: A regression where a single-result bag returns [] or throws would not be caught.

Suggestion: Extend OfType_Should_Return_CorrectObject or add a dedicated test:

PropertyBag bag = new();
DummyProperty single = new();
bag.Add(single);
bag.Add(PassedTestNodeStateProperty.CachedInstance);
TProperty[] result = bag.OfType<DummyProperty>();
Assert.HasCount(1, result);
Assert.AreSame(single, result[0]);

}

/// <summary>
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27 changes: 27 additions & 0 deletions test/UnitTests/Microsoft.Testing.Platform.UnitTests/Messages/PropertyBagTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -121,6 +121,33 @@ public void OfType_Should_Return_CorrectObject()

Assert.AreEqual(PassedTestNodeStateProperty.CachedInstance, property.OfType<TestNodeStateProperty>().Single());
Assert.HasCount(2, property.OfType<DummyProperty>());

// No DummyProperty2 in the bag — exercises the "no match found" path in the while-loop
Assert.IsEmpty(property.OfType<DummyProperty2>());
}

[TestMethod]
public void OfType_WithSingleMatch_ReturnsSingleItemArray()
{
PropertyBag property = new();
DummyProperty singleProperty = new();
property.Add(singleProperty);
property.Add(PassedTestNodeStateProperty.CachedInstance);

DummyProperty[] result = property.OfType<DummyProperty>();

Assert.HasCount(1, result);
Assert.AreSame(singleProperty, result[0]);
}

[TestMethod]
public void OfType_WithOnlyTestNodeStateProperty_ReturnsEmpty()
{
PropertyBag property = new();
property.Add(PassedTestNodeStateProperty.CachedInstance);

// _property is null; _testNodeStateProperty is set — exercises the new early-return path
Assert.IsEmpty(property.OfType<DummyProperty>());
}

[TestMethod]
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