[Perf Improver] perf: reduce allocations in test discovery and data-driven test execution (#7818)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

src/Adapter/MSTestAdapter.PlatformServices/Execution/TestMethodRunner.cs

@@ -321,10 +321,19 @@ private async Task<TestResult[]> ExecuteTestWithDataSourceAsync(UTF.ITestDataSou
             data = tupleExpandedToArray;
         }
 
-        displayName = displayNameFromTestDataRow
-            ?? testDataSource?.GetDisplayName(new ReflectionTestMethodInfo(_testMethodInfo.MethodInfo, _test.DisplayName), data)
-            ?? (testDataSource is null ? displayName : TestDataSourceUtilities.ComputeDefaultDisplayName(new ReflectionTestMethodInfo(_testMethodInfo.MethodInfo, _test.DisplayName), data))
-            ?? displayName;
+        // PERF: Extract ReflectionTestMethodInfo to avoid allocating it twice when testDataSource is not null
+        // and both GetDisplayName and ComputeDefaultDisplayName need to be consulted.
+        if (displayNameFromTestDataRow is null && testDataSource is not null)
+        {
+            var reflectionMethodInfo = new ReflectionTestMethodInfo(_testMethodInfo.MethodInfo, _test.DisplayName);
+            displayName = testDataSource.GetDisplayName(reflectionMethodInfo, data)
+                ?? TestDataSourceUtilities.ComputeDefaultDisplayName(reflectionMethodInfo, data)
+                ?? displayName;
+        }
+        else
+        {
+            displayName = displayNameFromTestDataRow ?? displayName;
+        }
 
         var stopwatch = Stopwatch.StartNew();
         _testMethodInfo.SetArguments(data);

src/Adapter/MSTestAdapter.PlatformServices/Services/TestSourceHandler.cs

@@ -52,19 +52,22 @@ internal sealed class TestSourceHandler : ITestSourceHandler
         ];
 #endif
 
-    /// <summary>
-    /// Gets the set of valid extensions for sources targeting this platform.
-    /// </summary>
-    public IEnumerable<string> ValidSourceExtensions => new List<string>
-            {
-                EngineConstants.DllExtension,
+    // PERF: Cached to avoid allocating a new list on every property access.
+    private static readonly IEnumerable<string> CachedValidSourceExtensions =
+        [
+            EngineConstants.DllExtension,
 #if NETFRAMEWORK
-                EngineConstants.PhoneAppxPackageExtension,
+            EngineConstants.PhoneAppxPackageExtension,
 #elif WINDOWS_UWP || WIN_UI
-                EngineConstants.AppxPackageExtension,
+            EngineConstants.AppxPackageExtension,
 #endif
-                EngineConstants.ExeExtension,
-            };
+            EngineConstants.ExeExtension,
+        ];
+
+    /// <summary>
+    /// Gets the set of valid extensions for sources targeting this platform.
+    /// </summary>
+    public IEnumerable<string> ValidSourceExtensions => CachedValidSourceExtensions;
 
     /// <summary>
     /// Verifies if the assembly provided is referenced by the source.