Optimize TestMethodRunner: fix double enumeration, reduce allocations

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

@@ -84,14 +84,15 @@ internal async Task<TestResult[]> ExecuteAsync(string? initializationLogs, strin
             }
 
 #pragma warning disable IDE0056 // Use index operator
+            TestResult lastResult = result[result.Length - 1];
             result[result.Length - 1] = new TestResult
             {
                 TestFailureException = new TestFailedException(UnitTestOutcome.Error, ex.TryGetMessage(), ex.TryGetStackTraceInformation()),
-                LogOutput = result[result.Length - 1].LogOutput,
-                LogError = result[result.Length - 1].LogError,
-                DebugTrace = result[result.Length - 1].DebugTrace,
-                TestContextMessages = result[result.Length - 1].TestContextMessages,
-                Duration = result[result.Length - 1].Duration,
+                LogOutput = lastResult.LogOutput,
+                LogError = lastResult.LogError,
+                DebugTrace = lastResult.DebugTrace,
+                TestContextMessages = lastResult.TestContextMessages,
+                Duration = lastResult.Duration,
             };
 #pragma warning restore IDE0056 // Use index operator
         }
@@ -167,7 +168,7 @@ internal async Task<TestResult[]> RunTestMethodAsync()
         // In case of data driven, set parent info in results.
         if (isDataDriven)
         {
-            results = UpdateResultsWithParentInfo(results);
+            UpdateResultsWithParentInfo(results);
         }
 
         // Set a result in case no result is present.
@@ -214,13 +215,13 @@ private async Task<bool> TryExecuteFoldedDataDrivenTestsAsync(List<TestResult> r
                 continue;
             }
 
-            IEnumerable<object?[]>? dataSource;
-
             // This code is to execute tests. To discover the tests code is in AssemblyEnumerator.ProcessTestDataSourceTests.
             // Any change made here should be reflected in AssemblyEnumerator.ProcessTestDataSourceTests as well.
-            dataSource = testDataSource.GetData(_testMethodInfo.MethodInfo);
+            IReadOnlyList<object?[]> dataSource = testDataSource.GetData(_testMethodInfo.MethodInfo) is IReadOnlyList<object?[]> dataList
+                ? dataList
+                : testDataSource.GetData(_testMethodInfo.MethodInfo).ToList();
 
-            if (!dataSource.Any())
+            if (dataSource.Count == 0)
             {
                 if (!MSTestSettings.CurrentSettings.ConsiderEmptyDataSourceAsInconclusive)
                 {
@@ -255,8 +256,7 @@ private async Task<bool> TryExecuteFoldedDataDrivenTestsAsync(List<TestResult> r
 
     private async Task ExecuteTestFromDataSourceAttributeAsync(List<TestResult> results)
     {
-        Stopwatch watch = new();
-        watch.Start();
+        var watch = Stopwatch.StartNew();
 
         try
         {
@@ -449,9 +449,9 @@ private static UnitTestOutcome GetAggregateOutcome(List<TestResult> results)
 
         // Get aggregate outcome.
         UnitTestOutcome aggregateOutcome = results[0].Outcome;
-        foreach (TestResult result in results)
+        for (int i = 1; i < results.Count; i++)
         {
-            aggregateOutcome = aggregateOutcome.GetMoreImportantOutcome(result.Outcome);
+            aggregateOutcome = aggregateOutcome.GetMoreImportantOutcome(results[i].Outcome);
         }
 
         return aggregateOutcome;
@@ -462,26 +462,12 @@ private static UnitTestOutcome GetAggregateOutcome(List<TestResult> results)
     /// Add parent results as first result in updated result.
     /// </summary>
     /// <param name="results">Results.</param>
-    /// <returns>Updated results which contains parent result as first result. All other results contains parent result info.</returns>
-    private static List<TestResult> UpdateResultsWithParentInfo(List<TestResult> results)
+    private static void UpdateResultsWithParentInfo(List<TestResult> results)
     {
-        // Return results in case there are no results.
-        if (results.Count == 0)
-        {
-            return results;
-        }
-
-        // UpdatedResults contain parent result at first position and remaining results has parent info updated.
-        var updatedResults = new List<TestResult>();
-
         foreach (TestResult result in results)
         {
             result.ExecutionId = Guid.NewGuid();
             result.ParentExecId = Guid.NewGuid();
-
-            updatedResults.Add(result);
         }
-
-        return updatedResults;
     }
 }