[efficiency-improver] perf: cache GetParameters() and ReflectionTestMethodInfo across data rows

[github-actions]

Goal and Rationale

Eliminate redundant ParameterInfo[] allocations in the data-driven test hot path. MethodInfo.GetParameters() is a CLR method that always returns a freshly allocated array (CLR safety guarantee). For a test with N data rows every row triggers one or more such allocations, creating O(N) heap pressure that is avoidable.

Focus area: Code-Level Efficiency — unnecessary object creation on a per-row hot path.

Approach

Three targeted changes:

1. ReflectionTestMethodInfo.GetParameters() — cache result

// Before
public override ParameterInfo[] GetParameters() => _methodInfo.GetParameters();

// After
private ParameterInfo[]? _parameters;
public override ParameterInfo[] GetParameters() => _parameters ??= _methodInfo.GetParameters();

ReflectionTestMethodInfo wraps an immutable MethodInfo and is used to compute row display names. The parameter list cannot change between calls, so caching is safe.

2. TestMethodInfo.ResolveArguments() — use cached ParameterTypes

// Before
ParameterInfo[] parametersInfo = MethodInfo.GetParameters();

// After
ParameterInfo[] parametersInfo = ParameterTypes;

PR #9514 added ParameterTypes (lazy-cached MethodInfo.GetParameters()) to TestMethodInfo, but ResolveArguments() was left calling the raw method, bypassing the cache. This fixes the oversight.

3. TestMethodRunner._cachedReflectionMethodInfo — reuse wrapper across rows

// Before (in ExecuteTestWithDataSourceAsync — called once per row)
var reflectionMethodInfo = new ReflectionTestMethodInfo(_testMethodInfo.MethodInfo, _test.DisplayName);

// After
_cachedReflectionMethodInfo ??= new ReflectionTestMethodInfo(_testMethodInfo.MethodInfo, _test.DisplayName);

_testMethodInfo.MethodInfo and _test.DisplayName are both immutable for the TestMethodRunner lifetime, so the wrapper can safely be cached as a field and shared across all data rows.

Energy Efficiency Evidence

Proxy metric used: Heap allocation count — directly maps to GC pressure and the CPU energy spent on GC collection cycles.

Scenario	Before	After
ReflectionTestMethodInfo instances per data-driven test	N	1
ParameterInfo[] from GetParameters() in display-name path	N	1
ParameterInfo[] from GetParameters() in ResolveArguments()	N	1

N = number of data rows. For a [DynamicData] test providing 100 rows, this reduces from ~300 short-lived heap objects (3 × N) to 3 total — a 99% reduction in these allocations.

Reproducibility: Run any data-driven MSTest test under a profiler (dotnet-trace / BenchmarkDotNet with MemoryDiagnoser) to observe allocation counts per row before and after this change.

Green Software Foundation Context

Hardware Efficiency / Demand Shaping: Reduced GC frequency means the runtime reclaims CPU resources for actual test execution rather than collection bookkeeping. On energy-proportional hardware, lower background CPU demand translates directly to lower power draw during test runs.

Trade-offs

• The cached ParameterInfo[] in ReflectionTestMethodInfo must not be mutated by callers. All existing call sites read the array without mutation (display-name formatting, parameter-count checks), so this is safe. The existing ITestMethod.ParameterTypes interface contract (which clones the array for external consumers) is unchanged.
• The _cachedReflectionMethodInfo field is null for non-data-driven tests, adding 8 bytes to TestMethodRunner instances with no behavioural change.

Test Status

• ✅ ./build.sh — build succeeded, 0 warnings
• ✅ ./build.sh -test — all unit tests passed (MTP-hosted suite)
• i️ MSTestAdapter-internal tests not run locally (CI-only; handled separately per repo convention)

🤖 Automated content by GitHub Copilot. Posted via a maintainer's GitHub token, so it appears under their account — the account owner did not write or approve this content personally. Generated by the Efficiency Improver workflow. · 177.3 AIC · ⌖ 21.4 AIC · ⊞ 13.6K · [◷]( · ◷)

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Show patch preview (110 of 110 lines)

From 4a4f8ce1bae6cea21822017e340049cf98731b51 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Sat, 4 Jul 2026 22:10:21 +0000
Subject: [PATCH] perf: cache GetParameters() and ReflectionTestMethodInfo
 across data rows

Three micro-optimisations that eliminate redundant ParameterInfo[] allocations
for every row in a data-driven test run:

1. ReflectionTestMethodInfo.GetParameters():
 MethodInfo.GetParameters() allocates a fresh ParameterInfo[] on every call
 (CLR safety guarantee). Cache with _parameters ??= _methodInfo.GetParameters()
 so all callers on the same wrapper share a single allocation.

2. TestMethodInfo.ResolveArguments():
 Was calling MethodInfo.GetParameters() directly, bypassing the cached
 TestMethodInfo.ParameterTypes property added in #9514. Switch to ParameterTypes.

3. TestMethodRunner._cachedReflectionMethodInfo:
 ExecuteTestWithDataSourceAsync() created a new ReflectionTestMethodInfo per
 data row. Since both wrapped MethodInfo and DisplayName are immutable for the
 TestMethodRunner lifetime, cache the wrapper so N rows share one instance.

Impact (proxy metric: heap allocations per data-driven test execution):
- Before: N ReflectionTestMethodInfo + N ParameterInfo[] from GetParameters()
 in the display-name path, plus N ParameterInfo[] in ResolveArguments()
- After: 1 ReflectionTestMethodInfo + 1 ParameterInfo[] shared across N rows

(N = number of data rows supplied by the ITestDataSource/DynamicData attribute)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../Execution/TestMethodInfo.ArgumentResolution.cs | 2 +-
 .../Execution/TestMethodRunner.cs | 12 +++++++++---
 .../Internal/ReflectionTestMethodInfo.cs | 6 +++++-
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/Adapter/MSTestAdapter.PlatformServices/Execution/TestMethodInfo.ArgumentResolution.cs b/src/Adapter/MSTestAdapter.PlatformS
... (truncated)