[Efficiency Improver] perf: skip PropertyBag construction in BFSTestNodeVisitor when filter has no property expressions

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Goal and Rationale

When BFSTestNodeVisitor walks the test tree with a TreeNodeFilter, it calls MatchesFilter for every node. Prior to this change, it always constructed a PropertyBag from the node's IProperty[] — even though the PropertyBag is only inspected when the filter contains [Trait=Value] property expressions.

A PropertyBag backed by N properties allocates 1 PropertyBag object + N Property linked-list nodes per call. In a tree of 1 000 test nodes, each carrying 3 properties, that is 4 000 short-lived heap objects created just to be immediately discarded for the common case where no property filter is active.

Focus Area

Code-Level Efficiency — eliminate unnecessary object creation in a per-node hot path.

Approach

1. TreeNodeFilter.ContainsPropertyFilters (new internal property) — computed once during filter parsing using _filters.Any(HasPropertyFilterExpression). A recursive helper HasPropertyFilterExpression walks the parsed FilterExpression tree looking for any ValueAndPropertyExpression node (the only kind that inspects PropertyBag contents at match time). Cost: one extra boolean field + O(depth × width) traversal at construction time — amortised to zero over the lifetime of the filter.

2. BFSTestNodeVisitor — when ContainsPropertyFilters is false, the new static EmptyPropertyBag singleton is reused instead of constructing a per-node bag. When true, a PropertyBag is constructed as before (no regression for users who do use property filters).

Energy Efficiency Evidence

Proxy metric: heap allocations per test-node traversal with a path-only TreeNodeFilter (e.g. /AssemblyName/ClassName/MethodName).

	Before	After
PropertyBag objects / node	1	0
Property linked-list nodes / node	N (≈3–5)	0
Total allocations / 1 000-node tree	~4 000–6 000	0

Reasoning: Fewer short-lived heap objects → less GC pressure → fewer GC pauses → lower CPU/energy draw per test run. This directly maps to the Hardware Efficiency principle from the Green Software Foundation: avoid unnecessary computation and allocation on the critical path.

The static EmptyPropertyBag is allocated exactly once (class static initialiser), so it adds no ongoing cost.

Trade-offs

• Minimal: the change adds one boolean field and one helper method to TreeNodeFilter, and changes two lines in BFSTestNodeVisitor. No new public API surface.
• EmptyPropertyBag is mutable; however, it is only ever read (never written to) via the MatchesFilter code path when ContainsPropertyFilters is false, so sharing is safe.

Reproducibility

export PATH="$PWD/.dotnet:$PATH"
dotnet test test/UnitTests/MSTest.Engine.UnitTests/MSTest.Engine.UnitTests.csproj -p:TargetFramework=net8.0 --filter "BFSTestNodeVisitor"
dotnet test test/UnitTests/Microsoft.Testing.Platform.UnitTests/Microsoft.Testing.Platform.UnitTests.csproj -p:TargetFramework=net8.0 --filter "TreeNodeFilter"

Test Status

• ✅ 10 / 10 BFSTestNodeVisitorTests pass (net8.0)
• ✅ 45 / 45 TreeNodeFilterTests pass (net8.0)

Note

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The changes have been pushed to branch efficiency/skip-propertybag-when-no-property-filter-37db331d9e78483b.

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Show patch preview (107 of 107 lines)

From 1b3325b8397454c41178beba09cbf32de0a56af8 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Tue, 28 Apr 2026 04:39:09 +0000
Subject: [PATCH] perf: skip PropertyBag construction in BFSTestNodeVisitor
 when filter has no property expressions
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Add ContainsPropertyFilters to TreeNodeFilter — computed once at parse time.
When false, BFSTestNodeVisitor reuses a static empty PropertyBag instead of
allocating a new PropertyBag (+ N Property linked-list nodes) per traversed
test node.

Proxy metric: heap allocations per test node during BFS traversal with a
TreeNodeFilter that contains no [Trait=Value] property conditions (the common
case).
  Before: 1 PropertyBag + N Property nodes per node (N = number of properties)
  After:  0 allocations (static empty bag reused)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../MSTest.Engine/Engine/BFSTestNodeVisitor.cs  | 17 +++++------------
 .../Requests/TreeNodeFilter/TreeNodeFilter.cs   | 12 ++++++++++++
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/src/Adapter/MSTest.Engine/Engine/BFSTestNodeVisitor.cs b/src/Adapter/MSTest.Engine/Engine/BFSTestNodeVisitor.cs
index dc98be1..d443281 100644
--- a/src/Adapter/MSTest.Engine/Engine/BFSTestNodeVisitor.cs
+++ b/src/Adapter/MSTest.Engine/Engine/BFSTestNodeVisitor.cs
@@ -11,6 +11,7 @@ namespace Microsoft.Testing.Framework;
 internal sealed class BFSTestNodeVisitor
 {
     private static readonly string PathSeparatorString = TreeNodeFilter.PathSeparator.ToString();
+    private static readonly PropertyBag EmptyPropertyBag = new();
 
     private readonly IEnumerable<TestNode> _rootTestNodes;
     private readonly ITestExecutionFilter _testExecutionFilter;
@@ -72,7 +73,10 @@ public async Task VisitAsync(Func<TestNode, TestNodeUid?, Task> onIncludedTestNo
             // When we are filtering as tr
... (truncated)