Deduplicate

src/NUnitEngine/nunit.engine.core/AsyncTestEngineResult.cs

@@ -22,6 +22,7 @@
 // ***********************************************************************
 
 using System;
+using System.ComponentModel;
 using System.Threading;
 using System.Xml;
 using NUnit.Common;
@@ -39,6 +40,21 @@ public class AsyncTestEngineResult : ITestRun
         private volatile TestEngineResult _result;
         private readonly ManualResetEvent _waitHandle = new ManualResetEvent(false);
 
+#if !NETSTANDARD1_6
+        public static AsyncTestEngineResult RunAsync(Func<TestEngineResult> func)
+        {
+            var testRun = new AsyncTestEngineResult();
+
+            using (var worker = new BackgroundWorker())
+            {
+                worker.DoWork += (sender, e) => testRun.SetResult(func.Invoke());
+                worker.RunWorkerAsync();
+            }
+
+            return testRun;
+        }
+#endif
+
         /// <summary>
         /// Get the result of this run.
         /// </summary>

src/NUnitEngine/nunit.engine.core/Polyfill.cs

@@ -0,0 +1,11 @@
+#if NET20
+
+namespace System
+{
+    // This would cause conflicts if it was public in the API assembly. This is an engine implementation detail since
+    // even though it's public because this assembly should not be compiled against by anyone that references the
+    // engine.
+    public delegate TResult Func<TResult>();
+}
+
+#endif

src/NUnitEngine/nunit.engine.core/Runners/AbstractTestRunner.cs

@@ -22,8 +22,6 @@
 // ***********************************************************************
 
 using System;
-using System.ComponentModel;
-using NUnit.Engine.Services;
 
 namespace NUnit.Engine.Runners
 {
@@ -110,19 +108,7 @@ public virtual void UnloadPackage()
         /// <returns>An <see cref="AsyncTestEngineResult"/> that will provide the result of the test execution</returns>
         protected virtual AsyncTestEngineResult RunTestsAsync(ITestEventListener listener, TestFilter filter)
         {
-            var testRun = new AsyncTestEngineResult();
-
-            using (var worker = new BackgroundWorker())
-            {
-                worker.DoWork += (s, ea) =>
-                {
-                    var result = RunTests(listener, filter);
-                    testRun.SetResult(result);
-                };
-                worker.RunWorkerAsync();
-            }
-
-            return testRun;
+            return AsyncTestEngineResult.RunAsync(() => RunTests(listener, filter));
         }
 #endif
 

src/NUnitEngine/nunit.engine/Services/TestAgency.AgentLease.cs

@@ -23,7 +23,6 @@
 
 #if !NETSTANDARD1_6 && !NETSTANDARD2_0
 using System;
-using System.ComponentModel;
 using System.Threading;
 
 namespace NUnit.Engine.Services
@@ -89,19 +88,7 @@ public TestEngineResult Run(ITestEventListener listener, TestFilter filter)
 
             public AsyncTestEngineResult RunAsync(ITestEventListener listener, TestFilter filter)
             {
-                var testRun = new AsyncTestEngineResult();
-
-                using (var worker = new BackgroundWorker())
-                {
-                    worker.DoWork += (s, ea) =>
-                    {
-                        var result = Run(listener, filter);
-                        testRun.SetResult(result);
-                    };
-                    worker.RunWorkerAsync();
-                }
-
-                return testRun;
+                return AsyncTestEngineResult.RunAsync(() => Run(listener, filter));
             }
 
             public void StopRun(bool force)